Zoom lens system, imaging device and camera

ABSTRACT

A zoom lens system comprising a first lens unit having negative power, a second lens unit having positive power and a third lens unit having positive power, wherein: the first lens unit comprises a first lens element having a concave surface at least on the image side and negative power and a second lens element having a convex surface at least on the object side and positive power; the second lens unit comprises a single third lens element, a cemented lens element of two lens elements having power of mutually different signs and a single sixth lens element; in zooming, all of the lens units move along an optical axis; and conditions (1): 5.0&lt;αi W &lt;20.0 and (I-2): n 11 ≧1.9 (where, 3.2&lt;f T /f W  and ω W &gt;35, αi W  is an incident angle of a principal ray to an image sensor at a maximum image height at a wide-angle limit, n 11  is a refractive index of the first lens element to the d-line, ω W  is a half view angle at a wide-angle limit, and f T  and f W  are focal lengths of the entire system at a telephoto limit and a wide-angle limit, respectively) are satisfied.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on application Nos. 2007-142629, 2007-142630and 2007-142631 filed in Japan on May 29, 2007, the contents of whichare hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a zoom lens system, an imaging deviceand a camera. In particular, the present invention relates to: a zoomlens system that has a remarkably reduced thickness at the time ofaccommodation so as to be suitable for a lens barrel of so-calledretraction type and that is still provided with a wide view angle at awide-angle limit and with a zooming ratio exceeding 3.2; an imagingdevice employing this zoom lens system; and a thin and compact cameraemploying this imaging device.

2. Description of the Background Art

Remarkably strong demands are present for size reduction of cameras suchas digital still cameras and digital video cameras (simply referred toas digital cameras, hereinafter) provided with an image sensor forperforming photoelectric conversion. In particular, in digital camerasprovided with a zoom lens system having a zooming ratio of 3 or thelike, which are most frequent in the number of sales in the market,popularity goes to a construction of external structure in which at thetime of accommodation (at the time of non-image taking), the overalllength of the lens barrel is reduced (lens barrel is retracted) so thatthe lens barrel itself does not protrude outside. Further, in recentyears, zoom lens systems are also desired that have a wide angle rangewhere the image taking field is large.

As zoom lens systems suitable for the above-mentioned digital cameras,for example, the following zoom lens systems are proposed.

For example, Japanese Laid-Open Patent Publication No. 2005-331860discloses a variable magnification optical system, in order from theobject side, including a first lens unit having negative optical powerand a second lens unit having positive optical power, wherein: at thetime of magnification change from a wide-angle limit to a telephotolimit, the interval between the first and the second lens units isreduced; the first lens unit is composed of two or more lenses; and atleast three lens units are each composed solely of a single lens or acemented lens.

Japanese Laid-Open Patent Publication No. 2006-011096 discloses avariable magnification optical system, in order from the object side,including a first lens unit having negative optical power and a secondlens unit having positive optical power each composed of a plurality oflenses, wherein: at the time of magnification change from a wide-anglelimit to a telephoto limit, the interval between the first and thesecond lens units is reduced; the first lens unit has at least oneaspheric surface; and a predetermined condition is satisfied by all ofthe maximum of the refractive index difference (absolute value) of thetwo lenses in the first lens unit, the composite focal length of thesecond lens unit, and the optical axial distance from the surface vertexof the most-image-sensor-side lens surface to the image sensor surfaceat a telephoto limit.

Japanese Laid-Open Patent Publication No. 2006-023679 discloses a zoomlens, in order from the object side to the image side, comprising afirst lens unit having negative refractive power and a second lens unithaving positive refractive power, wherein: the interval between the twolens units varies during the zooming; the first lens unit comprises alens 11 having negative refractive power and a lens 12 having positiverefractive power; the second lens unit comprises a lens 21 havingpositive refractive power and a lens 22 having negative refractivepower; and the Abbe numbers of the lens 21 and the lens 22 satisfy apredetermined condition.

Japanese Laid-Open Patent Publication No. 2006-065034 discloses a zoomlens, in order from the object side to the image side, comprising afirst lens unit having negative refractive power, a second lens unithaving positive refractive power and a third lens unit having positiverefractive power, wherein: the intervals between the individual lensunits vary during the zooming; the first lens unit is composed of onenegative lens and one positive lens; the second lens unit comprises asecond-a lens unit composed of one positive lens and one negative lensand a second-b lens unit that is arranged on the image side of thesecond-a lens unit and that has at least one positive lens; the thirdlens unit has at least one positive lens; and a predetermined conditionis satisfied by the image magnifications at a wide-angle limit and atelephoto limit of the second lens unit, the interval between the firstand the second lens units at a wide-angle limit, and the intervalbetween the second and the third lens units at a telephoto limit.

Japanese Laid-Open Patent Publication No. 2006-084829 discloses a zoomlens, in order from the object side to the image side, comprising afirst lens unit having negative refractive power, a second lens unithaving positive refractive power and a third lens unit having positiverefractive power, wherein: the intervals between the individual lensunits vary during the zooming; the second lens unit comprises a second-alens unit composed of, in order from the object side to the image side,a positive lens and a negative lens and a second-b lens unit that isarranged on the image side of the second-a lens unit and that has atleast one positive lens; and a predetermined condition is satisfied bythe half view angle at a wide-angle limit, the focal lengths of thefirst and the second lens units and the focal length of the entiresystem at a wide-angle limit.

Japanese Laid-Open Patent Publication No. 2006-139187 discloses a zoomlens, in order from the object side, comprising a first lens unit havingnegative refractive power, a second lens unit having positive refractivepower and a third lens unit having positive refractive power, wherein:the intervals between the individual lens units are changed so thatvariable magnification is achieved; the second lens unit is composed oftwo lens components consisting of a single lens on the object side and alens component on the image side; and a predetermined condition issatisfied by the radii of curvature of the single lens on the objectside and the image side and the lens optical axial thickness of thesingle lens.

Japanese Laid-Open Patent Publication No. 2006-171421 discloses a zoomlens, in order from the object side to the image side, comprising afirst lens unit having negative refractive power, a second lens unithaving positive refractive power and a third lens unit having positiverefractive power, wherein: the intervals between the individual lensunits vary during the zooming; the first lens unit, in order from theobject side to the image side, comprises one negative lens and onepositive lens; the second lens unit, in order from the object side tothe image side, comprises a positive lens, a positive lens, a negativelens and a positive lens; and during the zooming from a wide-angle limitto a telephoto limit, the third lens unit moves to the image side.

Japanese Laid-Open Patent Publication No. 2006-208890 discloses a zoomlens, in order from the object side to the image side, comprising afirst lens unit having negative refractive power, a second lens unithaving positive refractive power and a third lens unit having positiverefractive power, wherein: the intervals between the individual lensunits vary during the zooming; and a predetermined condition issatisfied by the amount of movement of the second lens unit during thezooming from a wide-angle limit to a telephoto limit, the intervalbetween the second and the third lens units at a wide-angle limit, thefocal lengths of the first and the second lens units and the focallength of the entire system at a wide-angle limit.

Japanese Laid-Open Patent Publication No. 2006-350027 discloses a zoomlens, in order from the object side, comprising at least a first lensunit composed of two components and a second lens unit composed of onecomponent, wherein: at the time of magnification change, at least theinterval between the first and the second lens units varies; the firstand the second lens units have aspheric surfaces; and a predeterminedcondition is satisfied by the paraxial radius of curvature of at leastone aspheric surface A of the first lens unit and the distance betweenthe intersecting point where the most off-axis principal ray passesthrough the aspheric surface A and the optical axis.

Japanese Laid-Open Patent Publication No. 2006-194974 discloses a zoomlens, in order from the object side to the image side, comprising afirst lens unit having negative refractive power and a second lens unithaving positive refractive power, wherein: the interval between theindividual units is changed so that magnification change from awide-angle limit to a telephoto limit is achieved; the first lens unitis, in order from the object side, composed of two lenses consisting ofa negative lens and a positive lens; and a predetermined condition issatisfied by the Abbe number of the positive lens, the refractive indexof the positive lens and the refractive index of the negative lens.

Japanese Laid-Open Patent Publication No. 2006-220715 discloses a zoomlens, in order from the object side, comprising a first lens unit havingnegative refractive power, a second lens unit having positive refractivepower and a third lens unit having positive refractive power, wherein:the intervals between the individual lens units are changed so thatvariable magnification is achieved; the first lens unit is composed oftwo lenses consisting of a negative lens and a positive lens; the secondlens unit comprises two positive lenses and one negative lens; the thirdlens unit is composed of one positive lens; and a predeterminedcondition is satisfied by the refractive index of the negative lens andthe refractive index of the positive lens in the first lens unit.

The optical systems disclosed in the above-mentioned publications havezooming ratios sufficient for application to digital cameras.Nevertheless, width of the view angle at a wide-angle limit and sizereduction are not simultaneously realized. In particular, from theviewpoint of size reduction, requirements in digital cameras of recentyears are not satisfied.

SUMMARY OF THE INVENTION

An object of the present invention is to realize: a zoom lens systemthat has a remarkably reduced thickness at the time of accommodation soas to be suitable for a lens barrel of so-called retraction type andthat is still provided with a wide view angle at a wide-angle limit andwith a zooming ratio of 3 or the like; an imaging device employing thiszoom lens system; and a thin and compact camera employing this imagingdevice.

The novel concepts disclosed herein were achieved in order to solve theforegoing problems in the conventional art, and herein is disclosed:

a zoom lens system, in order from the object side to the image side,comprising a first lens unit having negative optical power, a secondlens unit having positive optical power and a third lens unit havingpositive optical power, wherein

the first lens unit is composed of two lens elements, in order from theobject side to the image side, comprising a first lens element that hasa concave surface at least on the image side and that has negativeoptical power and a second lens element that has a convex surface atleast on the object side and that has positive optical power,

the second lens unit, in order from the object side to the image side,comprises a third lens element being one single lens element, a cementedlens element fabricated by cementing a fourth lens element and a fifthlens element having optical power of mutually different signs, and asixth lens element being one single lens element,

in zooming from a wide-angle limit to a telephoto limit, all of thefirst lens unit, the second lens unit and the third lens unit move alongan optical axis, and

the following conditions (1) and (I-2) are satisfied:5.0<αi_(W)<20.0  (1)n₁₁≧1.9  (I-2)

(here, 3.2<f_(T)/f_(W) and ω_(W)>35)

where,

αi_(W) is an incident angle of a principal ray to an image sensor at amaximum image height at a wide-angle limit (defined as positive when theprincipal ray is incident on a light acceptance surface of the imagesensor in a state of departing from the optical axis),

n₁₁ is a refractive index of the first lens element to the d-line,

ω_(W) is a half view angle (°) at a wide-angle limit,

f_(T) is a focal length of the entire system at a telephoto limit, and

f_(W) is a focal length of the entire system at a wide-angle limit.

The novel concepts disclosed herein were achieved in order to solve theforegoing problems in the conventional art, and herein is disclosed:

an imaging device capable of outputting an optical image of an object asan electric image signal, comprising:

a zoom lens system that forms the optical image of the object; and

an image sensor that converts the optical image formed by the zoom lenssystem into the electric image signal, wherein

in the zoom lens system,

the system, in order from the object side to the image side, comprises afirst lens unit having negative optical power, a second lens unit havingpositive optical power and a third lens unit having positive opticalpower, wherein

the first lens unit is composed of two lens elements, in order from theobject side to the image side, comprising a first lens element that hasa concave surface at least on the image side and that has negativeoptical power and a second lens element that has a convex surface atleast on the object side and that has positive optical power,

the second lens unit, in order from the object side to the image side,comprises a third lens element being one single lens element, a cementedlens element fabricated by cementing a fourth lens element and a fifthlens element having optical power of mutually different signs, and asixth lens element being one single lens element,

in zooming from a wide-angle limit to a telephoto limit, all of thefirst lens unit, the second lens unit and the third lens unit move alongan optical axis, and

the following conditions (1) and (I-2) are satisfied:5.0<αi_(W)<20.0  (1)n₁₁≧1.9  (I-2)

(here, 3.2<f_(T)/f_(W) and ω_(W)>35)

where,

αi_(W) is an incident angle of a principal ray to an image sensor at amaximum image height at a wide-angle limit (defined as positive when theprincipal ray is incident on a light acceptance surface of the imagesensor in a state of departing from the optical axis),

n₁₁ is a refractive index of the first lens element to the d-line,

ω_(W) is a half view angle (°) at a wide-angle limit,

f_(T) is a focal length of the entire system at a telephoto limit, and

f_(W) is a focal length of the entire system at a wide-angle limit.

The novel concepts disclosed herein were achieved in order to solve theforegoing problems in the conventional art, and herein is disclosed:

a camera for converting an optical image of an object into an electricimage signal and then performing at least one of displaying and storingof the converted image signal, comprising

an imaging device having a zoom lens system that forms the optical imageof the object and an image sensor that converts the optical image formedby the zoom lens system into the electric image signal, wherein

in the zoom lens system,

the system, in order from the object side to the image side, comprises afirst lens unit having negative optical power, a second lens unit havingpositive optical power and a third lens unit having positive opticalpower, wherein

the first lens unit is composed of two lens elements, in order from theobject side to the image side, comprising a first lens element that hasa concave surface at least on the image side and that has negativeoptical power and a second lens element that has a convex surface atleast on the object side and that has positive optical power,

the second lens unit, in order from the object side to the image side,comprises a third lens element being one single lens element, a cementedlens element fabricated by cementing a fourth lens element and a fifthlens element having optical power of mutually different signs, and asixth lens element being one single lens element,

in zooming from a wide-angle limit to a telephoto limit, all of thefirst lens unit, the second lens unit and the third lens unit move alongan optical axis, and

the following conditions (1) and (I-2) are satisfied:5.0<αi_(W)<20.0  (1)n₁₁≧1.9  (I-2)

(here, 3.2<f_(T)/f_(W) and ω_(W)>35)

where,

αi_(W) is an incident angle of a principal ray to an image sensor at amaximum image height at a wide-angle limit (defined as positive when theprincipal ray is incident on a light acceptance surface of the imagesensor in a state of departing from the optical axis),

n₁₁ is a refractive index of the first lens element to the d-line,

ω_(W) is a half view angle (°) at a wide-angle limit,

f_(T) is a focal length of the entire system at a telephoto limit, and

f_(W) is a focal length of the entire system at a wide-angle limit.

The novel concepts disclosed herein were achieved in order to solve theforegoing problems in the conventional art, and herein is disclosed:

a zoom lens system, in order from the object side to the image side,comprising a first lens unit having negative optical power, a secondlens unit having positive optical power and a third lens unit havingpositive optical power, wherein

the first lens unit is composed of two lens elements, in order from theobject side to the image side, comprising a first lens element that hasa concave surface at least on the image side and that has negativeoptical power and a second lens element that has a convex surface atleast on the object side and that has positive optical power,

the second lens unit, in order from the object side to the image side,comprises a third lens element being one single lens element, a cementedlens element fabricated by cementing a fourth lens element and a fifthlens element having optical power of mutually different signs, and asixth lens element being one single lens element,

in zooming from a wide-angle limit to a telephoto limit, all of thefirst lens unit, the second lens unit and the third lens unit move alongan optical axis, and

the following conditions (1) and (II-2) are satisfied:5.0<αi_(W)<20.0  (1)(n ₁₁−1)·(n ₁₂−1)≧0.84  (II-2)

(here, 3.2<f_(T)/f_(W) and ω_(W)>35)

where,

αi_(W) is an incident angle of a principal ray to an image sensor at amaximum image height at a wide-angle limit (defined as positive when theprincipal ray is incident on a light acceptance surface of the imagesensor in a state of departing from the optical axis),

n₁₁ is a refractive index of the first lens element to the d-line,

n₁₂ is a refractive index of the second lens element to the d-line,

ω_(W) is a half view angle (°) at a wide-angle limit,

f_(T) is a focal length of the entire system at a telephoto limit, and

f_(W) is a focal length of the entire system at a wide-angle limit.

The novel concepts disclosed herein were achieved in order to solve theforegoing problems in the conventional art, and herein is disclosed:

an imaging device capable of outputting an optical image of an object asan electric image signal, comprising:

a zoom lens system that forms the optical image of the object; and

an image sensor that converts the optical image formed by the zoom lenssystem into the electric image signal, wherein

in the zoom lens system,

the system, in order from the object side to the image side, comprises afirst lens unit having negative optical power, a second lens unit havingpositive optical power and a third lens unit having positive opticalpower, wherein

the first lens unit is composed of two lens elements, in order from theobject side to the image side, comprising a first lens element that hasa concave surface at least on the image side and that has negativeoptical power and a second lens element that has a convex surface atleast on the object side and that has positive optical power,

the second lens unit, in order from the object side to the image side,comprises a third lens element being one single lens element, a cementedlens element fabricated by cementing a fourth lens element and a fifthlens element having optical power of mutually different signs, and asixth lens element being one single lens element,

in zooming from a wide-angle limit to a telephoto limit, all of thefirst lens unit, the second lens unit and the third lens unit move alongan optical axis, and

the following conditions (1) and (II-2) are satisfied:5.0<αi_(W)<20.0  (1)(n ₁₁−1)·(n ₁₂−1)≧0.84  (II-2)

(here, 3.2<f_(T)/f_(W) and ω_(W)>35)

where,

αi_(W) is an incident angle of a principal ray to an image sensor at amaximum image height at a wide-angle limit (defined as positive when theprincipal ray is incident on a light acceptance surface of the imagesensor in a state of departing from the optical axis),

n₁₁ is a refractive index of the first lens element to the d-line,

n₁₂ is a refractive index of the second lens element to the d-line,

ω_(W) is a half view angle (°) at a wide-angle limit,

f_(T) is a focal length of the entire system at a telephoto limit, and

f_(W) is a focal length of the entire system at a wide-angle limit.

The novel concepts disclosed herein were achieved in order to solve theforegoing problems in the conventional art, and herein is disclosed:

a camera for converting an optical image of an object into an electricimage signal and then performing at least one of displaying and storingof the converted image signal, comprising

an imaging device having a zoom lens system that forms the optical imageof the object and an image sensor that converts the optical image formedby the zoom lens system into the electric image signal, wherein

in the zoom lens system,

the system, in order from the object side to the image side, comprises afirst lens unit having negative optical power, a second lens unit havingpositive optical power and a third lens unit having positive opticalpower, wherein

the first lens unit is composed of two lens elements, in order from theobject side to the image side, comprising a first lens element that hasa concave surface at least on the image side and that has negativeoptical power and a second lens element that has a convex surface atleast on the object side and that has positive optical power,

the second lens unit, in order from the object side to the image side,comprises a third lens element being one single lens element, a cementedlens element fabricated by cementing a fourth lens element and a fifthlens element having optical power of mutually different signs, and asixth lens element being one single lens element,

in zooming from a wide-angle limit to a telephoto limit, all of thefirst lens unit, the second lens unit and the third lens unit move alongan optical axis, and

the following conditions (1) and (II-2) are satisfied:5.0<αi_(W)<20.0  (1)(n ₁₁−1)·(n ₁₂−1)≧0.84  (II-2)

(here, 3.2<f_(T)/f_(W) and ω_(W)>35)

where,

αi_(W) is an incident angle of a principal ray to an image sensor at amaximum image height at a wide-angle limit (defined as positive when theprincipal ray is incident on a light acceptance surface of the imagesensor in a state of departing from the optical axis),

n₁₁ is a refractive index of the first lens element to the d-line,

n₁₂ is a refractive index of the second lens element to the d-line,

ω_(W) is a half view angle (°) at a wide-angle limit,

f_(T) is a focal length of the entire system at a telephoto limit, and

f_(W) is a focal length of the entire system at a wide-angle limit.

The novel concepts disclosed herein were achieved in order to solve theforegoing problems in the conventional art, and herein is disclosed:

a zoom lens system, in order from the object side to the image side,comprising a first lens unit having negative optical power, a secondlens unit having positive optical power and a third lens unit havingpositive optical power, wherein

the first lens unit is composed of two lens elements, in order from theobject side to the image side, comprising a first lens element that hasa concave surface at least on the image side and that has negativeoptical power and a second lens element that has a convex surface atleast on the object side and that has positive optical power,

the second lens unit, in order from the object side to the image side,comprises a third lens element being one single lens element, a cementedlens element fabricated by cementing a fourth lens element and a fifthlens element having optical power of mutually different signs, and asixth lens element being one single lens element,

in zooming from a wide-angle limit to a telephoto limit, all of thefirst lens unit, the second lens unit and the third lens unit move alongan optical axis, and

the following conditions (1) and (III-2) are satisfied:5.0<αi_(W)<20.0  (1)n₁₂≧2.1  (III-2)

(here, 3.2<f_(T)/f_(W) and ω_(W)>35)

where,

αi_(W) is an incident angle of a principal ray to an image sensor at amaximum image height at a wide-angle limit (defined as positive when theprincipal ray is incident on a light acceptance surface of the imagesensor in a state of departing from the optical axis),

n₁₂ is a refractive index of the second lens element to the d-line,

ω_(W) is a half view angle (°) at a wide-angle limit,

f_(T) is a focal length of the entire system at a telephoto limit, and

f_(W) is a focal length of the entire system at a wide-angle limit.

The novel concepts disclosed herein were achieved in order to solve theforegoing problems in the conventional art, and herein is disclosed:

an imaging device capable of outputting an optical image of an object asan electric image signal, comprising:

a zoom lens system that forms the optical image of the object; and

an image sensor that converts the optical image formed by the zoom lenssystem into the electric image signal, wherein

in the zoom lens system,

the system, in order from the object side to the image side, comprises afirst lens unit having negative optical power, a second lens unit havingpositive optical power and a third lens unit having positive opticalpower, wherein

the first lens unit is composed of two lens elements, in order from theobject side to the image side, comprising a first lens element that hasa concave surface at least on the image side and that has negativeoptical power and a second lens element that has a convex surface atleast on the object side and that has positive optical power,

the second lens unit, in order from the object side to the image side,comprises a third lens element being one single lens element, a cementedlens element fabricated by cementing a fourth lens element and a fifthlens element having optical power of mutually different signs, and asixth lens element being one single lens element,

in zooming from a wide-angle limit to a telephoto limit, all of thefirst lens unit, the second lens unit and the third lens unit move alongan optical axis, and

the following conditions (1) and (III-2) are satisfied:5.0<αi_(W)<20.0  (1)n₁₂≧2.1  (III-2)

(here, 3.2<f_(T)/f_(W) and ω_(W)>35)

where,

αi_(W) is an incident angle of a principal ray to an image sensor at amaximum image height at a wide-angle limit (defined as positive when theprincipal ray is incident on a light acceptance surface of the imagesensor in a state of departing from the optical axis),

n₁₂ is a refractive index of the second lens element to the d-line,

ω_(W) is a half view angle (°) at a wide-angle limit,

f_(T) is a focal length of the entire system at a telephoto limit, and

f_(W) is a focal length of the entire system at a wide-angle limit.

The novel concepts disclosed herein were achieved in order to solve theforegoing problems in the conventional art, and herein is disclosed:

a camera for converting an optical image of an object into an electricimage signal and then performing at least one of displaying and storingof the converted image signal, comprising

an imaging device having a zoom lens system that forms the optical imageof the object and an image sensor that converts the optical image formedby the zoom lens system into the electric image signal, wherein

in the zoom lens system,

the system, in order from the object side to the image side, comprises afirst lens unit having negative optical power, a second lens unit havingpositive optical power and a third lens unit having positive opticalpower, wherein

the first lens unit is composed of two lens elements, in order from theobject side to the image side, comprising a first lens element that hasa concave surface at least on the image side and that has negativeoptical power and a second lens element that has a convex surface atleast on the object side and that has positive optical power,

the second lens unit, in order from the object side to the image side,comprises a third lens element being one single lens element, a cementedlens element fabricated by cementing a fourth lens element and a fifthlens element having optical power of mutually different signs, and asixth lens element being one single lens element,

in zooming from a wide-angle limit to a telephoto limit, all of thefirst lens unit, the second lens unit and the third lens unit move alongan optical axis, and

the following conditions (1) and (III-2) are satisfied:5.0<αi_(W)<20.0  (1)n₁₂≧2.1  (III-2)

(here, 3.2<f_(T)/f_(W) and ω_(W)>35)

where,

αi_(W) is an incident angle of a principal ray to an image sensor at amaximum image height at a wide-angle limit (defined as positive when theprincipal ray is incident on a light acceptance surface of the imagesensor in a state of departing from the optical axis),

n₁₂ is a refractive index of the second lens element to the d-line,

ω_(W) is a half view angle (°) at a wide-angle limit,

f_(T) is a focal length of the entire system at a telephoto limit, and

f_(W) is a focal length of the entire system at a wide-angle limit.

The present invention can provide a zoom lens system that has aremarkably reduced thickness at the time of accommodation so as to besuitable for a lens barrel of so-called retraction type and that isstill provided with a wide view angle at a wide-angle limit and with azooming ratio exceeding 3.2. Further, according to the presentinvention, an imaging device employing this zoom lens system and a thinand compact camera employing this imaging device can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

This and other objects and features of this invention will become clearfrom the following description, taken in conjunction with the preferredembodiments with reference to the accompanied drawings in which:

FIGS. 1 a-1 c are lens arrangement diagrams showing an infinity in-focuscondition of a zoom lens system according to Embodiments I-1, II-1 andIII-1 (Examples I-1, II-1 and III-1);

FIGS. 2 a-2 c are longitudinal aberration diagrams showing an infinityin-focus condition of a zoom lens system according to Examples I-1, II-1and III-1;

FIG. 3 is a lateral aberration diagram in a basic state where image blurcompensation is not performed and in an image blur compensation state ata telephoto limit of a zoom lens system according to Examples I-1, II-1and III-1;

FIGS. 4 a-4 c are lens arrangement diagrams showing an infinity in-focuscondition of a zoom lens system according to Embodiments I-2, II-2 andIII-2 (Examples I-2, II-2 and III-2);

FIGS. 5 a-5 c are longitudinal aberration diagrams showing an infinityin-focus condition of a zoom lens system according to Examples I-2, II-2and III-2;

FIG. 6 is a lateral aberration diagram in a basic state where image blurcompensation is not performed and in an image blur compensation state ata telephoto limit of a zoom lens system according to Examples I-2, II-2and III-2;

FIG. 7 is a schematic configuration diagram of a digital still cameraaccording to Embodiments I-3, II-3 and III-3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments I-1 to I-2, II-1 toII-2 and III-1 to III-2

FIG. 1 is a lens arrangement diagram of a zoom lens system according toEmbodiments I-1, II-1 and III-1. FIG. 4 is a lens arrangement diagram ofa zoom lens system according to Embodiments I-2, II-2 and III-2.

FIGS. 1 and 4 show respectively a zoom lens system in an infinityin-focus condition. In each figure, part (a) shows a lens configurationat a wide-angle limit (in the minimum focal length condition: focallength f_(W)), part (b) shows a lens configuration at a middle position(in an intermediate focal length condition: focal lengthf_(M)=√(f_(W)·f_(T))), and part (c) shows a lens configuration at atelephoto limit (in the maximum focal length condition: focal lengthf_(T)). Further, in each figure, straight or curved arrows providedbetween part (a) and part (b) show the movement of each lens unit fromthe wide-angle limit to the telephoto limit through the middle position.Moreover, in each figure, an arrow provided to a lens unit indicatesfocusing from an infinity in-focus condition to a close-object focusingstate, that is, the moving direction at the time of focusing from aninfinity in-focus condition to a close-object focusing state.

The zoom lens system according to each embodiment, in order from theobject side to the image side, comprises a first lens unit G1 havingnegative optical power, a second lens unit G2 having positive opticalpower and a third lens unit G3 having positive optical power. Then, inzooming from a wide-angle limit to a telephoto limit, the first lensunit G1, the second lens unit G2 and the third lens unit G3 all movealong the optical axis (this lens configuration is referred to as thebasic configuration of the embodiments, hereinafter). In the zoom lenssystem according to each embodiment, these lens units are arranged intoa desired optical power arrangement, so that a zooming ratio exceeding3.2 and high optical performance are achieved and still size reductionis realized in the entire lens system.

In FIGS. 1 and 4, an asterisk “*” provided to a particular surfaceindicates that the surface is aspheric. Further, in each figure, asymbol (+) or (−) provided to the sign of each lens unit corresponds tothe sign of optical power of the lens unit. Moreover, in each figure,the straight line located on the most right-hand side indicates theposition of an image surface S. On the object side relative to the imagesurface S (between the image surface S and each of the most image sidelens surfaces of third lens unit G3), two plane parallel plates such asoptical low-pass filters and face plates of an image sensor areprovided. Moreover, in each figure, a diaphragm A is provided betweenthe most image side lens surface of the first lens unit G1 and each ofthe most object side lens surfaces of the second lens unit G2.

As shown in FIG. 1, in the zoom lens system according to Embodiment I-1,the first lens unit G1, in order from the object side to the image side,comprises: a negative meniscus first lens element L1 with the convexsurface facing the object side; and a positive meniscus second lenselement L2 with the convex surface facing the object side. The firstlens element L1 has a refractive index to the d-line as high as 1.9 orgreater.

Further, in the zoom lens system according to Embodiment II-1, the firstlens unit G1, in order from the object side to the image side,comprises: a negative meniscus first lens element L1 with the convexsurface facing the object side; and a positive meniscus second lenselement L2 with the convex surface facing the object side. The firstlens element L1 and the second lens element L2 have high refractiveindices to the d-line.

Further, in the zoom lens system according to Embodiment III-1, thefirst lens unit G1, in order from the object side to the image side,comprises: a negative meniscus first lens element L1 with the convexsurface facing the object side; and a positive meniscus second lenselement L2 with the convex surface facing the object side. The secondlens element L2 has a refractive index to the d-line as high as 2.1 orgreater.

In each zoom lens system according to Embodiments I-1, II-1 and III-1,the second lens unit G2, in order from the object side to the imageside, comprises: a positive meniscus third lens element L3 with theconvex surface facing the object side; a bi-convex fourth lens elementL4; a bi-concave fifth lens element L5; and a bi-convex sixth lenselement L6. Among these, the fourth lens element L4 and the fifth lenselement L5 are cemented with each other.

Further, in each zoom lens system according to Embodiments I-1, II-1 andIII-1, the third lens unit G3 comprises solely a bi-convex seventh lenselement L7.

Here, in each zoom lens system according to Embodiments I-1, II-1 andIII-1, parallel plates L8 and L9 are, in order from the object side tothe image side, provided on the object side relative to the imagesurface S (between the image surface S and the seventh lens element L7).

In each zoom lens system according to Embodiments I-1, II-1 and III-1,in zooming from a wide-angle limit to a telephoto limit, the first lensunit G1 moves with locus of a convex to the image side with changing theinterval with the second lens unit G2, while the second lens unit G2moves to the object side, and while the third lens unit G3 moves to theimage side.

In the zoom lens system according to Embodiment I-1, in particular, asshown later in Table I-7, the first lens element L1 that constitutes thefirst lens unit G1 and that has a concave surface on the image side andnegative optical power is provided with a high refractive index. Thus,in the first lens element L1, when the thickness of a part where thelight ray height is great is set up appropriately, the lens thickness,especially, the edge thickness, can be reduced. Accordingly, the zoomlens system according to Embodiment I-1 has a reduced overall opticallength at the time of non-use.

In the zoom lens system according to Embodiment II-1, in particular, asshown later in Table II-7, the first lens element L1 having a concavesurface on the image side and negative optical power and the second lenselement L2 having a convex surface on the object side and positiveoptical power, which constitute the first lens unit G1, have highrefractive indices. As such, when both of the first lens element L1 andthe second lens element L2 have high refractive indices, the opticalaxial lens thicknesses of these lens elements can be reduced, while theradii of curvature of the lenses can be increased. Further, when therefractive index difference of these lens elements is reduced, controlof the Petzval sum becomes easy. This permits appropriate compensationof curvature of field. Further, aberration compensation can be performedwithout the necessity of using a surface having a small radius ofcurvature and hence strong optical power. This permits easy compensationof off-axial aberration, especially, distortion and astigmatism at awide-angle limit, which easily causes a problem especially in a zoomlens system having a wide view angle at a wide-angle limit.

In the zoom lens system according to Embodiment III-1, in particular, asshown later in Table III-7, the second lens element L2 that constitutesthe first lens unit G1 and that has a convex surface on the object sideand positive optical power is provided with a remarkably high refractiveindex. Thus, in the second lens element L2, the optical axial lensthickness can be reduced, while the radius of curvature of the lens canbe increased. Accordingly, the zoom lens system according to EmbodimentIII-1 has a reduced overall optical length at the time of non-use.

Further, in each zoom lens system according to Embodiments I-1, II-1 andIII-1, the second lens unit G2 comprises: a third lens element L3 beinga single lens element; a cemented lens element fabricated by cementing afourth lens element L4 having positive optical power and a fifth lenselement L5 having negative optical power; and a sixth lens element L6being a single lens element. Thus, in each zoom lens system according toEmbodiments I-1, II-1 and III-1, change of axial spherical aberration atthe time of magnification change can be compensated appropriately.Further, like in each zoom lens system according to Embodiments I-1,II-1 and III-1, when the entire optical power is increased by employinga glass material having a high refractive index in the first lens unitG1, the incident angle of the principal ray that enters the second lensunit G2 increases. However, when the second lens unit G2 has theabove-mentioned configuration, off-axial aberration generated in such acase can be compensated appropriately. Thus, the interval between thefirst lens unit G1 and the second lens unit G2 can be reduced, so thatsize reduction of each zoom lens system can be realized. Further, it ispreferable that like in each zoom lens system according to EmbodimentsI-1, II-1 and III-1, the object side surfaces of the third lens elementL3 and the fourth lens element L4 are convex and the image side surfaceof the fifth lens element L5 is concave. According to thisconfiguration, axial spherical aberration and off-axial coma aberrationcan simultaneously be compensated satisfactory.

As shown in FIG. 4, in the zoom lens system according to Embodiment I-2,the first lens unit G1, in order from the object side to the image side,comprises: a negative meniscus first lens element L1 with the convexsurface facing the object side; and a positive meniscus second lenselement L2 with the convex surface facing the object side. The firstlens element L1 has a refractive index to the d-line as high as 1.9 orgreater.

Further, in the zoom lens system according to Embodiment II-2, the firstlens unit G1, in order from the object side to the image side,comprises: a negative meniscus first lens element L1 with the convexsurface facing the object side; and a positive meniscus second lenselement L2 with the convex surface facing the object side. The firstlens element L1 and the second lens element L2 have high refractiveindices to the d-line.

Further, in the zoom lens system according to Embodiment III-2, thefirst lens unit G1, in order from the object side to the image side,comprises: a negative meniscus first lens element L1 with the convexsurface facing the object side; and a positive meniscus second lenselement L2 with the convex surface facing the object side. The secondlens element L2 has a refractive index to the d-line as high as 2.1 orgreater.

In each zoom lens system according to Embodiments I-2, II-2 and III-2,the second lens unit G2, in order from the object side to the imageside, comprises: a positive meniscus third lens element L3 with theconvex surface facing the object side; a bi-convex fourth lens elementL4; a bi-concave fifth lens element L5; and a bi-convex sixth lenselement L6. Among these, the fourth lens element L4 and the fifth lenselement L5 are cemented with each other.

Further, in each zoom lens system according to Embodiments I-2, II-2 andIII-2, the third lens unit G3 comprises solely a bi-convex seventh lenselement L7.

Here, in each zoom lens system according to Embodiments I-2, II-2 andIII-2, parallel plates L8 and L9 are, in order from the object side tothe image side, provided on the object side relative to the imagesurface S (between the image surface S and the seventh lens element L7).

In each zoom lens system according to Embodiments I-2, II-2 and III-2,in zooming from a wide-angle limit to a telephoto limit, the first lensunit G1 moves with locus of a convex to the image side with changing theinterval with the second lens unit G2, while the second lens unit G2moves to the object side, and while the third lens unit G3 moves to theimage side.

In the zoom lens system according to Embodiment I-2, in particular, asshown later in Table I-7, the first lens element L1 that constitutes thefirst lens unit G1 and that has a concave surface on the image side andnegative optical power is provided with a high refractive index. Thus,in the first lens element L1, when the thickness of a part where thelight ray height is great is set up appropriately, the lens thickness,especially, the edge thickness, can be reduced. Accordingly, the zoomlens system according to Embodiment I-2 has a reduced overall opticallength at the time of non-use.

In the zoom lens system according to Embodiment II-2, in particular, asshown later in Table II-7, the first lens element L1 having a concavesurface on the image side and negative optical power and the second lenselement L2 having a convex surface on the object side and positiveoptical power, which constitute the first lens unit G1, have highrefractive indices. As such, when both of the first lens element L1 andthe second lens element L2 have high refractive indices, the opticalaxial lens thicknesses of these lens elements can be reduced, while theradii of curvature of the lenses can be increased. Further, when therefractive index difference of these lens elements is reduced, controlof the Petzval sum becomes easy. This permits appropriate compensationof curvature of field. Further, aberration compensation can be performedwithout the necessity of using a surface having a small radius ofcurvature and hence strong optical power. This permits easy compensationof off-axial aberration, especially, distortion and astigmatism at awide-angle limit, which easily causes a problem especially in a zoomlens system having a wide view angle at a wide-angle limit.

In the zoom lens system according to Embodiment III-2, in particular, asshown later in Table III-7, the second lens element L2 that constitutesthe first lens unit G1 and that has a convex surface on the object sideand positive optical power is provided with a remarkably high refractiveindex. Thus, in the second lens element L2, the optical axial lensthickness can be reduced, while the radius of curvature of the lens canbe increased. Accordingly, the zoom lens system according to EmbodimentIII-2 has a reduced overall optical length at the time of non-use.

Further, in each zoom lens system according to Embodiments I-2, II-2 andIII-2, the second lens unit G2 comprises: a third lens element L3 beinga single lens element; a cemented lens element fabricated by cementing afourth lens element L4 having positive optical power and a fifth lenselement L5 having negative optical power; and a sixth lens element L6being a single lens element. Thus, in each zoom lens system according toEmbodiments I-2, II-2 and III-2, change of axial spherical aberration atthe time of magnification change can be compensated appropriately.Further, like in each zoom lens system according to Embodiments I-2,II-2 and III-2, when the entire optical power is increased by employinga glass material having a high refractive index in the first lens unitG1, the incident angle of the principal ray that enters the second lensunit G2 increases. However, when the second lens unit G2 has theabove-mentioned configuration, off-axial aberration generated in such acase can be compensated appropriately. Thus, the interval between thefirst lens unit G1 and the second lens unit G2 can be reduced, so thatsize reduction of each zoom lens system can be realized. Further, it ispreferable that like in each zoom lens system according to EmbodimentsI-2, II-2 and III-2, the object side surfaces of the third lens elementL3 and the fourth lens element L4 are convex and the image side surfaceof the fifth lens element L5 is concave. According to thisconfiguration, axial spherical aberration and off-axial coma aberrationcan simultaneously be compensated satisfactory.

In the zoom lens system according to each embodiment, in zooming from awide-angle limit to a telephoto limit, the first lens unit G1, thesecond lens unit G2 and the third lens unit G3 all move along theoptical axis. Also, among these lens units, for example, the second lensunit G2 is moved in a direction perpendicular to the optical axis, sothat image blur caused by hand blurring, vibration and the like can becompensated optically.

In the present invention, when the image blur is to be compensatedoptically, the second lens unit moves in a direction perpendicular tothe optical axis as described above, so that image blur is compensatedin a state that size increase in the entire zoom lens system issuppressed and a compact construction is realized and that excellentimaging characteristics such as small decentering coma aberration anddecentering astigmatism are satisfied.

Conditions are described below that are preferable to be satisfied by azoom lens system having the above-mentioned basic configuration likeeach zoom lens system according to Embodiments I-1 to I-2, II-1 to II-2and III-1 to III-2. Here, a plurality of preferable conditions are setforth for the zoom lens system according to each embodiment. Aconstruction that satisfies all the plural conditions is most desirablefor the zoom lens system. However, when an individual condition issatisfied, a zoom lens system having the corresponding effect can beobtained.

Further, all conditions described below hold only under the followingtwo premise conditions (A) and (B), unless noticed otherwise.3.2<f _(T) /f _(W)  (A)ω_(W)>35  (B)

where,

ω_(W) is a half view angle (°) at a wide-angle limit,

f_(T) is a focal length of the entire system at a telephoto limit, and

f_(W) is a focal length of the entire system at a wide-angle limit.

Here, the condition (B) is replaced by the following condition (B)′, theeffect obtained by virtue of each condition described below is achievedmore successfully.ω_(W)>38  (B)′

In a zoom lens system having the above-mentioned basic configurationlike each zoom lens system according to Embodiments I-1 to I-2, II-1 toII-2 and III-1 to III-2, the following condition (1) is satisfied.5.0<αi_(W)<20.0  (1)

where,

αi_(W) is an incident angle of a principal ray to an image sensor at amaximum image height at a wide-angle limit (defined as positive when theprincipal ray is incident on a light acceptance surface of the imagesensor in a state of departing from the optical axis).

The condition (1) sets forth the incident angle of the principal ray tothe image sensor at the maximum image height at a wide-angle limit. Whenthe condition (1) is satisfied, the incident angle at which the mostoff-axis principal ray enters the image sensor becomes small. Thisreduces the influence of shading. When the value exceeds the upper limitof the condition (1), the influence of shading in the image sensorreduces the amount of periphery light. In contrast, when the value goesbelow the lower limit of the condition (1), the angle of the negativemost off-axis principal ray at a telephoto limit becomes large at thetime of magnification change. This reduces the amount of periphery lightespecially a telephoto limit.

Here, the following condition (1)′ is further satisfied, a change issuppressed in the incident angle of the principal ray to the imagesensor at the maximum image height during the zooming. This reduces alsoa fluctuation in the amount of periphery light. Thus, this situation isremarkably effective.αi_(W)<15.0  (1)′

Here, in a zoom lens system having the above-mentioned basicconfiguration like each zoom lens system according to Embodiments I-1 toI-2, the following condition (I-2) is satisfied simultaneously to theabove-mentioned condition (1).n₁₁≧1.9  (I-2)

where,

n₁₁ is a refractive index of the first lens element to the d-line.

The condition (I-2) sets forth the refractive index of the first lenselement. When the condition (I-2) is satisfied, the center thickness ofthe first lens element is reduced. Further, even when the curvature,especially, the curvature on the image side, is not increased, curvatureof field on the wide-angle side is suppressed. Further, when thecondition (I-2) is satisfied, a shape can be ensured that is effectiveespecially for compensation of distortion and astigmatism at awide-angle limit.

In a zoom lens system having the above-mentioned basic configurationlike each zoom lens system according to Embodiments I-1 to I-2, it ispreferable that the following condition (I-3) is satisfied.0.8<(n ₁₁−1)²<1.5  (I-3)

where,

n₁₁ is a refractive index of the first lens element to the d-line.

The condition (I-3) sets forth the refractive index of the first lenselement. When the condition (I-3) is satisfied, the center thickness ofthe first lens element is reduced. Further, even when the curvature,especially, the curvature on the image side, is not increased, curvatureof field on the wide-angle side is suppressed. Further, when thecondition (I-3) is satisfied, a shape can be ensured that is effectiveespecially for compensation of distortion and astigmatism at awide-angle limit. Here, in the first lens element, it is preferable thatin a state that the above-mentioned condition (I-3) is satisfied, theimage side surface is made aspheric. When the image side surface of thefirst lens element is made aspheric, off-axial aberration, especially,distortion and astigmatism at a wide-angle limit, can be compensatedeffectively.

In a zoom lens system having the above-mentioned basic configurationlike each zoom lens system according to Embodiments I-1 to I-2, it ispreferable that the following condition (I-4) is satisfied.0.75<(n ₁₁−1)·f _(W) /r ₁₂<1.2  (I-4)

where,

r₁₂ is a radius of curvature of the image side surface of the first lenselement,

n₁₁ is a refractive index of the first lens element to the d-line, and

f_(W) is a focal length of the entire system at a wide-angle limit.

The condition (I-4) sets forth the refractive index of the first lenselement. When the value exceeds the upper limit of the condition (I-4),the radius of curvature of the image side surface of the first lenselement becomes excessively small, and hence fabrication becomesdifficult. Thus, this situation is not preferable. In contrast, when thevalue goes below the lower limit of the condition (I-4), the opticalpower of the image side surface of the first lens element becomesexcessively weak. Thus, compensation of the above-mentioned off-axialaberration, especially, distortion and astigmatism at a wide-anglelimit, becomes insufficient. Accordingly, this situation is notpreferable. Here, in the first lens element, it is preferable that in astate that the above-mentioned condition (I-4) is satisfied, the imageside surface is made aspheric. When the image side surface of the firstlens element is made aspheric, off-axial aberration, especially,distortion and astigmatism at a wide-angle limit, can be compensatedeffectively.

Further, in a zoom lens system having the above-mentioned basicconfiguration like each zoom lens system according to Embodiments II-1to II-2, the following condition (II-2) is satisfied simultaneously tothe above-mentioned condition (1).(n ₁₁−1)·(n ₁₂−1)≧0.84  (II-2)

where,

n₁₁ is a refractive index of the first lens element to the d-line, and

n₁₂ is a refractive index of the second lens element to the d-line.

The condition (II-2) sets forth the refractive indices of the first lenselement and the second lens element. When the condition (II-2) issatisfied, the optical axial lens thicknesses of these lens elements canbe reduced, while the radii of curvature of the lenses can be increased.Further, when the condition (II-2) is satisfied, control of the Petzvalsum by means of reducing the refractive index difference of these lenselements becomes easy. Thus, in a zoom lens system having the basicconfiguration, adjustment is performed such that the range of thecondition (II-2) should not be exceeded. Here, it is preferable that thefirst lens element satisfies the above-mentioned condition (II-2) andsimultaneously has an aspheric image side surface and that the secondlens element satisfies the above-mentioned condition (II-2) andsimultaneously has an aspheric object side surface. As such, when thetwo opposing surfaces of the first lens element and the second lenselement are made aspheric, off-axial aberration, especially, distortionand astigmatism at a wide-angle limit, can be compensated effectively.

Further, in a zoom lens system having the above-mentioned basicconfiguration like each zoom lens system according to Embodiments III-1to III-2, the following condition (III-2) is satisfied simultaneously tothe above-mentioned condition (1).n₁₂≧2.1  (III-2)

where,

n₁₂ is a refractive index of the second lens element to the d-line.

The condition (III-2) sets forth the refractive index of the second lenselement. When the condition (III-2) is satisfied, the center thicknessof the second lens element is reduced. Further, even when the curvature,especially, the curvature on the object side, is not increased,curvature of field on the wide-angle side is suppressed. Further, whenthe condition (III-2) is satisfied, a shape can be ensured that iseffective especially for compensation of distortion and astigmatism at awide-angle limit.

In a zoom lens system having the above-mentioned basic configurationlike each zoom lens system according to Embodiments III-1 to III-2, itis preferable that the following condition (III-3) is satisfied.0.8<(n ₁₂−1)²<1.5  (III-3)

where,

n₁₂ is a refractive index of the second lens element to the d-line.

The condition (III-3) sets forth the refractive index of the second lenselement. When the condition (III-3) is satisfied, the center thicknessof the second lens element is reduced. Further, even when the curvature,especially, the curvature on the image side, is not increased, curvatureof field on the wide-angle side is suppressed. Further, when thecondition (III-3) is satisfied, a shape can be ensured that is effectiveespecially for compensation of distortion and astigmatism at awide-angle limit. Here, in the second lens element, it is preferablethat in a state that the above-mentioned condition (III-3) is satisfied,the object side surface is made aspheric. When the object side surfaceof the second lens element is made aspheric, off-axial aberration,especially, distortion and astigmatism at a wide-angle limit, can becompensated effectively.

In a zoom lens system having the above-mentioned basic configurationlike each zoom lens system according to Embodiments III-1 to III-2, itis preferable that the following condition (III-4) is satisfied.0.4<(n ₁₂−1)·f _(W) /r ₂₁<0.7  (III-4)

where,

r₂₁ is a radius of curvature of the object side surface of the secondlens element,

n₁₂ is a refractive index of the second lens element to the d-line, and

f_(W) is a focal length of the entire system at a wide-angle limit.

The condition (III-4) sets forth the refractive index of the second lenselement. When the condition (III-4) is satisfied, the center thicknessof the second lens element is reduced. Further, even when the curvature,especially, the curvature on the image side, is not increased, curvatureof field on the wide-angle side is suppressed. Further, when thecondition (III-4) is satisfied, a shape can be ensured that is effectiveespecially for compensation of distortion and astigmatism at awide-angle limit. Here, in the second lens element, it is preferablethat in a state that the above-mentioned condition (III-4) is satisfied,the object side surface is made aspheric. When the object side surfaceof the second lens element is made aspheric, off-axial aberration,especially, distortion and astigmatism at a wide-angle limit, can becompensated effectively.

In a zoom lens system having the above-mentioned basic configurationlike each zoom lens system according to Embodiments I-1 to I-2, II-1 toII-2 and III-1 to III-2, it is preferable that the following condition(5) is satisfied.0.1<(n ₁₁−1)·(n ₁₂−1)·d·f _(W)/(r ₁₂ ·r ₂₁)<0.3  (5)

where,

n₁₁ is a refractive index of the first lens element to the d-line,

n₁₂ is a refractive index of the second lens element to the d-line,

r₁₂ is a radius of curvature of the image side surface of the first lenselement,

r₂₁ is a radius of curvature of the object side surface of the secondlens element,

d is an optical axial distance between the image side surface of thefirst lens element and the object side surface of the second lenselement, and

f_(W) is a focal length of the entire system at a wide-angle limit.

The condition (5) is to be satisfied by the first lens element and thesecond lens element in the first lens unit. When the value exceeds theupper limit of the condition (5), the thickness along the optical axisof the first lens unit increases, and hence difficulty arises inreduction of the overall length at the time of retraction. Thus, thissituation is not preferable. Further, when the value exceeds the upperlimit of the condition (5), compensation of various kinds of aberrationon the off-axial ray, especially, astigmatism and distortion at awide-angle limit, becomes insufficient. Thus, this situation is notpreferable. In contrast, when the value goes below the lower limit ofthe condition (5), similarly, compensation of various kinds ofaberration on the off-axial ray, especially, astigmatism and distortionat a wide-angle limit, becomes difficult. Thus, this situation is notpreferable.

Here, when at least one of the following conditions (5)′ and (5)″ issatisfied, the above-mentioned effect is achieved more successfully.0.15<(n ₁₁−1)·(n ₁₂−1)·d·f _(W)/(r ₁₂ ·r ₂₁)  (5)′(n ₁₁−1)·(n ₁₂−1)·d·f _(W)/(r ₁₂ ·r ₂₁)<0.25  (5)″

In a zoom lens system having the above-mentioned basic configurationlike each zoom lens system according to Embodiments I-1 to I-2, II-1 toII-2 and III-1 to III-2, it is preferable that the following condition(6) is satisfied.0.0001<(n ₁₁−1)·(n ₁₂−1)·d ² ·f _(W)/(r ₁₂ ·r ₂₁ ·f _(t))<0.04  (6)

where,

n₁₁ is a refractive index of the first lens element to the d-line,

n₁₂ is a refractive index of the second lens element to the d-line,

r₁₂ is a radius of curvature of the image side surface of the first lenselement,

r₂₁ is a radius of curvature of the object side surface of the secondlens element,

d is an optical axial distance between the image side surface of thefirst lens element and the object side surface of the second lenselement,

f_(T) is a focal length of the entire system at a telephoto limit, and

f_(W) is a focal length of the entire system at a wide-angle limit.

The condition (6) is to be satisfied by the first lens element and thesecond lens element in the first lens unit. When the value exceeds theupper limit of the condition (6), the thickness along the optical axisof the first lens unit increases, and hence difficulty arises inreduction of the overall length at the time of retraction. Thus, thissituation is not preferable. Further, when the value exceeds the upperlimit of the condition (6), compensation of various kinds of aberrationon the off-axial ray, especially, astigmatism and distortion at awide-angle limit, becomes insufficient. Thus, this situation is notpreferable. In contrast, when the value goes below the lower limit ofthe condition (6), similarly, compensation of various kinds ofaberration on the off-axial ray, especially, astigmatism and distortionat a wide-angle limit, becomes difficult. Thus, this situation is notpreferable.

In a zoom lens system having the above-mentioned basic configurationlike each zoom lens system according to Embodiments I-1 to I-2, II-1 toII-2 and III-1 to III-2, it is preferable that the following condition(9) is satisfied.2.4<|f _(G1) |/f _(W)<4.0  (9)

where,

f_(G1) is a composite focal length of the first lens unit, and

f_(W) is a focal length of the entire system at a wide-angle limit.

The condition (9) sets forth the focal length of the first lens unit.When the value exceeds the upper limit of the condition (9), the opticalpower of the first lens unit becomes excessively weak. Thus,compensation of various kinds of aberration on the off-axial ray,especially, astigmatism and distortion at a wide-angle limit, becomesinsufficient. Further, the effective diameter of the first lens unitneed be increased. Thus, size reduction becomes difficult especially ina direction perpendicular to the optical axis. Accordingly, thissituation is not preferable. In contrast, when the value goes below thelower limit of the condition (9), the optical power of the first lensunit becomes excessively strong, and hence decentering error sensitivitybetween the first lens element and the second lens element in the firstlens unit becomes high. As a result, performance degradation caused bydecentering increases, so that fabrication becomes difficult. Thus, thissituation is not preferable. Further, when the value goes below thelower limit of the condition (9), magnification chromatic aberrationgenerated in the first lens unit becomes excessively large. Thus, thissituation is not preferable.

When the following condition (9)′ is satisfied, the above-mentionedeffect is achieved more successfully.|f _(G1) |/f _(W)<3.0  (9)′

In a zoom lens system having the above-mentioned basic configurationlike each zoom lens system according to Embodiments I-1 to I-2, II-1 toII-2 and III-1 to III-2, it is preferable that the following condition(10) is satisfied.1.85<f _(G2) /f _(W)<3.0  (10)

where,

f_(G2) is a composite focal length of the second lens unit, and

f_(W) is a focal length of the entire system at a wide-angle limit.

The condition (10) sets forth the focal length of the second lens unit.When the value exceeds the upper limit of the condition (10), the amountof movement of the second lens unit during the zooming need beexcessively large. Thus, size reduction of the zoom lens system becomesdifficult. Accordingly, this situation is not preferable. In contrast,when the value goes below the lower limit of the condition (10), thefocal length of the second lens unit becomes excessively short. Thiscauses difficulty in aberration compensation for the entire variablemagnification range. Thus, this situation is not preferable.

Here, when any one of the following conditions (10)′ and (10)″ isfurther satisfied, the above-mentioned effect is achieved moresuccessfully.1.9<f _(G2) /f _(W)  (10)′1.95<f _(G2) /f _(W)  (10)″

In a zoom lens system having the above-mentioned basic configurationlike each zoom lens system according to Embodiments I-1 to I-2, II-1 toII-2 and III-1 to III-2, it is preferable that the following condition(11) is satisfied.2.5<f _(G3) /f _(W)<6.0  (11)

where,

f_(G3) is a composite focal length of the third lens unit, and

f_(W) is a focal length of the entire system at a wide-angle limit.

The condition (11) sets forth the focal length of the third lens unit.When the value exceeds the upper limit of the condition (11), theoptical power of the third lens unit is reduced, and hence the amount ofmovement of the third lens unit increases. Thus, size reduction of theoptical system becomes difficult. Accordingly, this situation is notpreferable. In contrast, when the value goes below the lower limit ofthe condition (11), the optical power of the third lens unit increases.This causes difficulty in compensation of spherical aberration and comaaberration in a variable magnification range where the third lens unitgoes comparatively close to the object side. Thus, this situation is notpreferable.

Here, when any one of the following conditions (11)′ and (11)″ isfurther satisfied, the above-mentioned effect is achieved moresuccessfully.3.0<f _(G3) /f _(W)  (11)′4.0<f _(G3) /f _(W)  (11)″

In a zoom lens system having the above-mentioned basic configurationlike each zoom lens system according to Embodiments I-1 to I-2, II-1 toII-2 and III-1 to III-2, it is preferable that the following condition(12) is satisfied.1.0<|f _(L1) |/f _(W)<2.5  (12)

where,

f_(L1) is a focal length of the first lens element, and

f_(W) is a focal length of the entire system at a wide-angle limit.

The condition (12) sets forth the focal length of the first lenselement. When the value exceeds the upper limit of the condition (12),compensation of various kinds of aberration on the off-axial ray,especially, astigmatism and distortion at a wide-angle limit, becomesinsufficient. Thus, this situation is not preferable. In contrast, whenthe value goes below the lower limit of the condition (12), the positiveoptical power of the second lens element that constitutes the first lensunit need be increased, and hence difficulty arises in compensation ofaberration generated in the first lens unit. Thus, this situation is notpreferable.

Here, when at least one of the following conditions (12)′ and (12)″ issatisfied, the above-mentioned effect is achieved more successfully.1.1<|f _(L1) |/f _(W)  (12)′|f _(L1) |/f _(W)<1.6  (12)″

In a zoom lens system having the above-mentioned basic configurationlike each zoom lens system according to Embodiments I-1 to I-2, II-1 toII-2 and III-1 to III-2, it is preferable that the following condition(13) is satisfied.2.0<f _(L2) /f _(W)<5.0  (13)

where,

f_(L2) is a focal length of the second lens element, and

f_(W) is a focal length of the entire system at a wide-angle limit.

The condition (13) sets forth the focal length of the second lenselement. When the value exceeds the upper limit of the condition (13),the Petzval sum increases excessively, and hence the curvature of fieldincreases. Further, astigmatism also increases excessively. Thus, thissituation is not preferable. In contrast, when the value goes below thelower limit of the condition (13), the negative optical power of thefirst entire lens unit becomes weak, and hence difficulty arises inachieving the size reduction of the zoom lens system. Thus, thissituation is not preferable.

Here, when at least one of the following conditions (13)′ and (13)″ issatisfied, the above-mentioned effect is achieved more successfully.2.4<f _(L2) /f _(W)  (13)′f _(L2) /f _(W)<4.0  (13)″

In a zoom lens system having the above-mentioned basic configurationlike each zoom lens system according to Embodiments I-1 to I-2, II-1 toII-2 and III-1 to III-2, it is preferable that the following condition(14) is satisfied.0.4<|f _(L1) |/|f _(G1)|<0.8  (14)

where,

f_(L1) is a focal length of the first lens element, and

f_(G1) is a composite focal length of the first lens unit.

The condition (14) sets forth the focal length of the first lenselement. When the value exceeds the upper limit of the condition (14),compensation of various kinds of aberration on the off-axial ray,especially, astigmatism and distortion at a wide-angle limit, becomesinsufficient. Thus, this situation is not preferable. In contrast, whenthe value goes below the lower limit of the condition (14), the positiveoptical power of the second lens element that constitutes the first lensunit need be increased, and hence difficulty arises in compensation ofaberration generated in the first lens unit. Thus, this situation is notpreferable.

Here, when any one of the following conditions (14)′ and (14)″ isfurther satisfied, the above-mentioned effect is achieved moresuccessfully.0.45<|f _(L1) |/|f _(G1)|  (14)′0.55<|f _(L1) |/|f _(G1)|  (14)″

In a zoom lens system having the above-mentioned basic configurationlike each zoom lens system according to Embodiments I-1 to I-2, II-1 toII-2 and III-1 to III-2, it is preferable that the following condition(15) is satisfied.0.85<f _(L2) /|f _(G1)|<2.0  (15)

where,

f_(L2) is a focal length of the second lens element, and

f_(G1) is a composite focal length of the first lens unit.

The condition (15) sets forth the focal length of the second lenselement. When the value exceeds the upper limit of the condition (15),the Petzval sum increases excessively, and hence the curvature of fieldincreases. Further, astigmatism also increases excessively. Thus, thissituation is not preferable. In contrast, when the value goes below thelower limit of the condition (15), the negative optical power of thefirst entire lens unit becomes weak, and hence difficulty arises inachieving the size reduction of the zoom lens system. Thus, thissituation is not preferable.

When the following condition (15)′ is satisfied, the above-mentionedeffect is achieved more successfully.f _(L2) /|f _(G1)|<1.8  (15)′

In a zoom lens system having the above-mentioned basic configurationlike each zoom lens system according to Embodiments I-1 to I-2, II-1 toII-2 and III-1 to III-2, it is preferable that the following condition(16) is satisfied.1.9<f _(L2) /|f _(L1)|<3.0  (16)

where,

f_(L1) is a focal length of the first lens element, and

f_(L2) is a focal length of the second lens element.

The condition (16) sets forth the ratio between the focal lengths of thefirst lens element and the second lens element. When the value exceedsthe upper limit of the condition (16), the optical power balance becomesunsatisfactory between the first lens element and the second lenselement, and hence curvature of field and distortion increase. Thus,this situation is not preferable. In contrast, when the value goes belowthe lower limit of the condition (16), similarly, the optical powerbalance becomes unsatisfactory between the first lens element and thesecond lens element, and hence distortion occurs. At the same time, theeffective diameter of the first lens element need be increased. Thus,size reduction becomes difficult especially in a direction perpendicularto the optical axis. Thus, this situation is not preferable.

When the following condition (16)′ is satisfied, the above-mentionedeffect is achieved more successfully.2.0<f _(L2) /|f _(L1)|  (16)′

Here, the lens units constituting the zoom lens system of eachembodiment are composed exclusively of refractive type lenses thatdeflect the incident light by refraction (that is, lenses of a type inwhich deflection is achieved at the interface between media each havinga distinct refractive index). However, the lens type is not limited tothis. For example, the lens units may employ diffractive type lensesthat deflect the incident light by diffraction; refractive-diffractivehybrid type lenses that deflect the incident light by a combination ofdiffraction and refraction; or gradient index type lenses that deflectthe incident light by distribution of refractive index in the medium.

Further, in each embodiment, a reflecting surface may be arranged in theoptical path so that the optical path may be bent before, after or inthe middle of the zoom lens system. The bending position may be set upin accordance with the necessity. When the optical path is bentappropriately, the apparent thickness of a camera can be reduced.

Moreover, each embodiment has been described for the case that aparallel plate such as an optical low-pass filter is arranged betweenthe last surface of the zoom lens system (the most image side surface ofthe third lens unit) and the image surface S. This low-pass filter maybe: a birefringent type low-pass filter made of, for example, a crystalwhose predetermined crystal orientation is adjusted; or a phase typelow-pass filter that achieves required characteristics of opticalcut-off frequency by diffraction.

Embodiments I-3, II-3 and III-3

FIG. 7 is a schematic construction diagram of a digital still cameraaccording to Embodiments I-3, II-3 and III-3. In FIG. 7, the digitalstill camera comprises: an imaging device having a zoom lens system 1and an image sensor 2 composed of a CCD; a liquid crystal displaymonitor 3; and a body 4. The employed zoom lens system 1 is a zoom lenssystem according to Embodiment I-1, II-1 or III-1. In FIG. 7, the zoomlens system 1 comprises a first lens unit G1, a diaphragm A, a secondlens unit G2 and a third lens unit G3. In the body 4, the zoom lenssystem 1 is arranged on the front side, while the image sensor 2 isarranged on the rear side of the zoom lens system 1. On the rear side ofthe body 4, the liquid crystal display monitor 3 is arranged, while anoptical image of a photographic object generated by the zoom lens system1 is formed on an image surface S.

A lens barrel comprises a main barrel 5, a moving barrel 6 and acylindrical cam 7. When the cylindrical cam 7 is rotated, the first lensunit G1, the second lens unit G2 and the third lens unit G3 move topredetermined positions relative to the image sensor 2, so thatmagnification change can be achieved ranging from a wide-angle limit toa telephoto limit. The third lens unit G3 is movable in an optical axisdirection by a motor for focus adjustment.

As such, when a zoom lens system according to Embodiment I-1, II-1 orIII-1 is employed in a digital still camera, a small digital stillcamera is obtained that has a high resolution and high capability ofcompensating the curvature of field and that has a short overall opticallength at the time of non-use. Here, in place of the zoom lens systemaccording to Embodiment I-1, II-1 or III-1, the digital still camerashown in FIG. 7 may employ any one of the zoom lens systems according toEmbodiments I-2, II-2 and III-2. Further, the optical system of thedigital still camera shown in FIG. 7 is applicable also to a digitalvideo camera for moving images. In this case, moving images with highresolution can be acquired in addition to still images.

Further, the above-mentioned zoom lens system according to EmbodimentsI-1 to I-2, II-1 to II-2 and III-1 to III-2 and an image sensor such asa CCD or a CMOS may be applied to a mobile telephone, a PDA (PersonalDigital Assistance), a surveillance camera in a surveillance system, aWeb camera, a vehicle-mounted camera or the like.

Numerical examples are described below in which the zoom lens systemsaccording to Embodiments I-1 to I-2, II-1 to II-2 and III-1 to III-2 areimplemented. Here, in the numerical examples, the units of length areall “mm”, while the units of view angle are all “°”. Moreover, in thenumerical examples, r is the radius of curvature, d is the axialdistance, nd is the refractive index to the d-line, and vd is the Abbenumber to the d-line. In the numerical examples, the surfaces markedwith * are aspherical surfaces, and the aspherical surface configurationis defined by the following expression.

$Z = {\frac{h^{2}/r}{1 + \sqrt{1 - {\left( {1 + k} \right)\left( {h/r} \right)^{2}}}} + {A\; 4\; h^{4}} + {A\; 6\; h^{6}} + {A\; 8\; h^{8}} + {A\; 10\; h^{10}} + {A\; 12\; h^{12}} + {A\; 14\; h^{14}}}$Here, κ is the conic constant. A4, A6, A8, A10, A12 and A14 are fourth,sixth, eighth, tenth, twelfth, fourteenth aspherical coefficients,respectively.

FIG. 2 is a longitudinal aberration diagram of a zoom lens systemaccording to Examples I-1, II-1 and III-1. FIG. 5 is a longitudinalaberration diagram of a zoom lens system according to Examples I-2, II-2and III-2.

In each longitudinal aberration diagram, part (a) shows the aberrationat a wide-angle limit, part (b) shows the aberration at a middleposition, and part (c) shows the aberration at a telephoto limit. Eachlongitudinal aberration diagram, in order from the left-hand side, showsthe spherical aberration (SA (mm)), the astigmatism (AST (mm)) and thedistortion (DIS (%)). In the spherical aberration diagram, the verticalaxis indicates the F-number (indicated as “F” in the figure), the solidline indicates the characteristics to the d-line, the short dashed lineindicates the characteristics to the F-line, and the long dashed lineindicates the characteristics to the C-line. In the astigmatism diagram,the vertical axis indicates the image height (indicated as “H” in thefigure), and the solid line and the dashed line indicate thecharacteristics to the sagittal image plane (indicated as “s” in thefigure) and the meridional image plane (indicated as “m” in the figure),respectively. In the distortion diagram, the vertical axis indicates theimage height (indicated as “H” in the figure).

Further, FIG. 3 is a lateral aberration diagram of a zoom lens systemaccording to Examples I-1, II-1 and III-1 at a telephoto limit. FIG. 6is a lateral aberration diagram of a zoom lens system according toExamples I-2, II-2 and III-2 at a telephoto limit.

In each lateral aberration diagram, the three upper aberration diagramscorrespond to a basic state where image blur compensation is notperformed at a telephoto limit, while the three lower aberrationdiagrams correspond to an image blur compensation state where the entiresecond lens unit G2 is moved with a predetermined amount in a directionperpendicular to the optical axis at a telephoto limit. Among thelateral aberration diagrams of the basic state, the upper one showslateral aberration at an image point of 70% of the maximum image height,the middle one shows lateral aberration at the axial image point, andthe lower one shows lateral aberration at an image point of −70% of themaximum image height. Among the lateral aberration diagrams of the imageblur compensation state, the upper one shows lateral aberration at animage point of 70% of the maximum image height, the middle one showslateral aberration at the axial image point, and the lower one showslateral aberration at an image point of −70% of the maximum imageheight. In each lateral aberration diagram, the horizontal axisindicates the distance from the principal ray on the pupil surface. Thesolid line indicates the characteristics to the d-line, the short dashedline indicates the characteristics to the F-line, and the long dashedline indicates the characteristics to the C-line. In each lateralaberration diagram, the meridional image plane is adopted as the planecontaining the optical axis of the first lens unit G1 and the opticalaxis of the second lens unit G2.

Here, the amount of movement of the second lens unit G2 in a directionperpendicular to the optical axis in the image blur compensation stateat a telephoto limit is as follows.

Examples I-1, II-1 and III-1: 0.100 mm

Examples I-2, II-2 and III-2: 0.100 mm

Here, when the shooting distance is infinity, at a telephoto limit, theamount of image decentering in a case that the zoom lens system inclinesby 0.6° is equal to the amount of image decentering in a case that theentire second lens unit G2 moves in parallel by each of theabove-mentioned values in a direction perpendicular to the optical axis.

As seen from the lateral aberration diagrams, satisfactory symmetry isobtained in the lateral aberration at the axial image point. Further,when the lateral aberration at the +70% image point and the lateralaberration at the −70% image point are compared with each other in thebasic state, all have a small degree of curvature and almost the sameinclination in the aberration curve. Thus, decentering coma aberrationand decentering astigmatism are small. This indicates that sufficientimaging performance is obtained even in the image blur compensationstate. Further, when the image blur compensation angle of a zoom lenssystem is the same, the amount of parallel movement required for imageblur compensation decreases with decreasing focal length of the entirezoom lens system. Thus, at arbitrary zoom positions, sufficient imageblur compensation can be performed for image blur compensation angles upto 0.6° without degrading the imaging characteristics.

Numerical Examples I-1, II-1 and III-1

The zoom lens systems of Numerical Examples I-1, II-1 and III-1correspond respectively to Embodiments I-1, II-1 and III-1 shown inFIG. 1. Table 1 shows the surface data of the zoom lens systems ofNumerical Examples I-1, II-1 and III-1. Table 2 shows the asphericaldata. Table 3 shows various data.

TABLE 1 (Surface data) Surface number r d nd vd Object surface ∞ ∞  151.08500 1.10000 1.90001 34.5  2* 6.68800 2.30000  3* 12.12200 1.750002.14001 17.0  4 21.50000 Variable  5 (Diaphragm) ∞ 0.35000  6* 5.700001.58700 1.80470 41.0  7 29.04600 0.37500  8 38.03700 1.04600 1.7291654.7  9 −16.50000 0.63000 1.76182 26.6 10 5.49100 0.70000 11* 17.681001.10000 1.66547 55.2 12 −20.90300 Variable 13* 33.43600 1.60000 1.6654755.2 14* −49.83400 Variable 15 ∞ 0.28000 1.51680 64.2 16 ∞ 0.50000 17 ∞0.50000 1.51680 64.2 18 ∞ 0.37000 19 ∞ 0.29815 Image surface ∞

TABLE 2 (Aspherical data) Surface No. 2 K = −1.56675E+00, A4 =4.70570E−04, A6 = 4.66416E−06, A8 = −9.97845E−07, A10 = 4.97712E−08, A12= −1.08769E−09, A14 = 8.99770E−12 Surface No. 3 K = 0.00000E+00, A4 =4.87626E−05, A6 = 2.01434E−06, A8 = −5.22735E−07, A10 = 2.72826E−08, A12= −6.10198E−10, A14 = 5.12805E−12 Surface No. 6 K = 0.00000E+00, A4 =−2.23822E−04, A6 = 7.67079E−06, A8 = −2.43773E−06, A10 = 4.29726E−07,A12 = −3.98936E−08, A14 = 1.56912E−09 Surface No. 11 K = 0.00000E+00, A4= −4.37904E−04, A6 = −5.27665E−05, A8 = 4.76568E−06, A10 = −6.52195E−07,A12 = 0.00000E+00, A14 = 0.00000E+00 Surface No. 13 K = 0.00000E+00, A4= −1.10340E−04, A6 = 1.04396E−05, A8 = −6.20441E−07, A10 = 1.92500E−08,A12 = −2.48363E−10, A14 = 0.00000E+00 Surface No. 14 K = 0.00000E+00, A4= 5.28184E−06, A6 = 1.04655E−07, A8 = −1.48869E−08, A10 = 0.00000E+00,A12 = 0.00000E+00, A14 = 0.00000E+00

TABLE 3 (Various data) Zooming ratio 3.28506 Wide-angle Middle Telephotolimit position limit Focal length 6.2096 13.2985 20.3990 F-number2.85034 4.26999 5.57319 View angle 38.7767 19.5485 12.8788 Image height4.6750 4.6750 4.6750 Overall length 40.4589 37.1496 40.0163 of lenssystem BF 0.09365 −0.50369 0.29815 d4 16.6839 5.4283 1.5000 d12 3.512313.7570 21.2901 d14 5.9810 4.2800 2.7400 Entrance pupil 8.6898 5.66013.8417 position Exit pupil −18.6236 −51.4459 −172.8086 position Frontprincipal 12.8393 15.4870 21.8369 points position Back principal 34.249223.8511 19.6172 points position Single lens data Lens Initial surfaceFocal element number length 1 1 −8.6520 2 3 22.1735 3 6 8.5536 4 815.9112 5 9 −5.3419 6 11 14.5598 7 13 30.3019 8 15 ∞ 9 17 ∞ Zoom lensunit data Initial Overall Lens surface Focal length of Front principalBack principal unit No. length lens unit points position points position1 1 −15.63371 5.15000 −0.20747 1.18551 2 5 12.54975 5.78800 −0.517991.29535 3 13 30.30192 1.60000 0.38874 1.02061

Numerical Examples I-2, II-2 and III-2

The zoom lens systems of Numerical Examples I-2, II-2 and III-2correspond respectively to Embodiments I-2, II-2 and III-2 shown in FIG.4. Table 4 shows the surface data of the zoom lens systems of NumericalExamples I-2, II-2 and III-2. Table 5 shows the aspherical data. Table 6shows various data.

TABLE 4 (Surface data) Surface number r d nd vd Object surface ∞ ∞  162.16200 1.10000 1.90001 34.5  2* 6.69200 2.30000  3* 12.07300 1.750002.14001 17.0  4 21.50000 Variable  5 (Diaphragm) ∞ 0.35000  6* 5.692001.58700 1.80470 41.0  7 32.03800 0.37500  8 29.47800 1.04600 1.7291654.7  9 −16.01700 0.63000 1.76182 26.6 10 5.39900 0.70000 11* 18.612001.10000 1.66547 55.2 12 −23.48300 Variable 13* 36.78300 1.60000 1.6654755.2 14* −48.34000 Variable 15 ∞ 0.28000 1.51680 64.2 16 ∞ 0.50000 17 ∞0.50000 1.51680 64.2 18 ∞ 0.37000 19 ∞ 0.28717 Image surface ∞

TABLE 5 (Aspherical data) Surface No. 2 K = −1.56154E+00, A4 =4.68480E−04, A6 = 4.15258E−06, A8 = −1.01913E−06, A10 = 5.05982E−08, A12= −1.06364E−09, A14 = 8.20851E−12 Surface No. 3 K = 0.00000E+00, A4 =5.16820E−05, A6 = 1.33836E−06, A8 = −5.23000E−07, A10 = 2.76838E−08, A12= −5.97362E−10, A14 = 4.65996E−12 Surface No. 6 K = 0.00000E+00, A4 =−2.38112E−04, A6 = 7.51411E−06, A8 = −2.40483E−06, A10 = 4.29616E−07,A12 = −4.01119E−08, A14 = 1.60238E−09 Surface No. 11 K = 0.00000E+00, A4= −5.17367E−04, A6 = −5.66448E−05, A8 = 4.53807E−06, A10 = −7.50402E−07,A12 = 0.00000E+00, A14 = 0.00000E+00 Surface No. 13 K = 0.00000E+00, A4= −6.25328E−05, A6 = 9.00851E−06, A8 = −7.82678E−07, A10 = 2.97351E−08,A12 = −4.15223E−10, A14 = 0.00000E+00 Surface No. 14 K = 0.00000E+00, A4= 6.42897E−05, A6 = −4.19023E−06, A8 = 6.58934E−08, A10 = 0.00000E+00,A12 = 0.00000E+00, A14 = 0.00000E+00

TABLE 6 (Various data) Zooming ratio 3.28135 Wide-angle Middle Telephotolimit position limit Focal length 6.2142 13.1141 20.3911 F-number2.85258 4.28066 5.64291 View angle 39.3679 19.8675 12.9178 Image height4.6750 4.6750 4.6750 Overall length 39.3161 36.6808 39.7421 of lenssystem BF 0.25556 −0.59241 0.28717 d4 15.8504 5.4283 1.5000 d12 3.041113.3769 21.0269 d14 5.9810 4.2800 2.7400 Entrance pupil 8.3349 5.56933.7979 position Exit pupil −17.5453 −46.5039 −132.8723 position Frontprincipal 12.3797 14.9375 21.0664 points position Back principal 33.101823.5667 19.3510 points position Single lens data Lens Initial surfaceFocal element number length 1 1 −8.4115 2 3 21.9794 3 6 8.3767 4 814.3722 5 9 −5.2338 6 11 15.7669 7 13 31.6266 8 15 ∞ 9 17 ∞ Zoom lensunit data Initial Overall Lens surface Focal length of Front principalBack principal unit No. length lens unit points position points position1 1 −15.04135 5.15000 −0.21859 1.17026 2 5 12.23158 5.78800 −0.682301.21868 3 13 31.62659 1.60000 0.41827 1.05031

Table I-7 shows values corresponding to the individual conditions in thezoom lens system of Numerical Examples I-1 to I-2. Table II-7 showsvalues corresponding to the individual conditions in the zoom lenssystem of Numerical Examples II-1 to II-2. Table III-7 shows valuescorresponding to the individual conditions in the zoom lens system ofNumerical Examples III-1 to III-2.

TABLE I-7 (Values corresponding to conditions) Numerical ExampleCondition I-1 I-2  (1) αi_(W) 11.82 12.45 (I-2) n₁₁ 1.90001 1.90001(I-3) (n₁₁ − 1)² 0.810 0.810 (I-4) (n₁₁ − 1) · f_(W)/r₁₂ 0.836 0.836 (5) (n₁₁ − 1) · (n₁₂ − 1) · d · f_(W)/(r₁₂ · r₂₁) 0.181 0.182  (6) (n₁₁− 1) · (n₁₂ − 1) · d² · f_(w)/(r₁₂ · r₂₁ · f_(T)) 0.020 0.020  (9)|f_(G1)|/f_(W) 2.518 2.420 (10) f_(G2)/f_(W) 2.021 1.968 (11)f_(G3)/f_(W) 4.880 5.089 (12) |f_(L1)|/f_(W) 1.393 1.354 (13)f_(L2)/f_(W) 3.571 3.537 (14) |f_(L1)|/|f_(G1)| 0.553 0.559 (15)f_(L2)/|f_(G1)| 1.418 1.461 (16) f_(L2)/|f_(L1)| 2.563 2.613

TABLE II-7 (Values corresponding to conditions) Numerical ExampleCondition II-1 II-2  (1) αi_(W) 11.82 12.45 (II-2) (n₁₁ − 1) · (n₁₂ − 1)1.026 1.026  (5) (n₁₁ − 1) · (n₁₂ − 1) · d · f_(W)/(r₁₂ · r₂₁) 0.1810.182  (6) (n₁₁ − 1) · (n₁₂ − 1) · d² · f_(w)/(r₁₂ · r₂₁ · f_(T)) 0.0200.020  (9) |f_(G1)|/f_(W) 2.518 2.420 (10) f_(G2)/f_(W) 2.021 1.968 (11)f_(G3)/f_(W) 4.880 5.089 (12) |f_(L1)|/f_(W) 1.393 1.354 (13)f_(L2)/f_(W) 3.571 3.537 (14) |f_(L1)|/|f_(G1)| 0.553 0.559 (15)f_(L2)/|f_(G1)| 1.418 1.461 (16) f_(L2)/|f_(L1)| 2.563 2.613

TABLE III-7 (Values corresponding to conditions) Numerical ExampleCondition III-1 III-2  (1) αi_(W) 11.82 12.45 (III-2) n₁₂ 2.140012.14001 (III-3) (n₁₂ − 1)² 1.300 1.300 (III-4) (n₁₂ − 1) · f_(W)/r₂₁0.584 0.587  (5) (n₁₁ − 1) · (n₁₂ − 1) · d · f_(W)/(r₁₂ · r₂₁) 0.1810.182  (6) (n₁₁ − 1) · (n₁₂ − 1) · d² · f_(w)/ 0.020 0.020 (r₁₂ · r₂₁ ·f_(T))  (9) |f_(G1)|/f_(W) 2.518 2.420 (10) f_(G2)/f_(W) 2.021 1.968(11) f_(G3)/f_(W) 4.880 5.089 (12) |f_(L1)|/f_(W) 1.393 1.354 (13)f_(L2)/f_(W) 3.571 3.537 (14) |f_(L1)|/|f_(G1)| 0.553 0.559 (15)f_(L2)/|f_(G1)| 1.418 1.461 (16) f_(L2)/|f_(L1)| 2.563 2.613

The zoom lens system according to the present invention is applicable toa digital input device such as a digital still camera, a digital videocamera, a mobile telephone, a PDA (Personal Digital Assistance), asurveillance camera in a surveillance system, a Web camera or avehicle-mounted camera. In particular, the present zoom lens system issuitable for an imaging optical system in a digital still camera, adigital video camera or the like that requires high image quality.

Although the present invention has been fully described by way ofexample with reference to the accompanying drawings, it is to beunderstood that various changes and modifications will be apparent tothose skilled in the art. Therefore, unless otherwise such changes andmodifications depart from the scope of the present invention, theyshould be construed as being included therein.

1. A zoom lens system, in order from the object side to the image side,comprising a first lens unit having negative optical power, a secondlens unit having positive optical power and a third lens unit havingpositive optical power, wherein the first lens unit, in order from theobject side to the image side, consists of a first lens element that hasa concave surface at least on the image side and that has negativeoptical power and a second lens element that has a convex surface atleast on the object side and that has positive optical power, the secondlens unit, in order from the object side to the image side, comprises athird lens element being one single lens element, a cemented lenselement fabricated by cementing a fourth lens element and a fifth lenselement having optical power of mutually different signs, and a sixthlens element being one single lens element, in zooming from a wide-anglelimit to a telephoto limit, all of the first lens unit, the second lensunit and the third lens unit move along an optical axis, and thefollowing conditions (1), (I-2) and (5) are satisfied:5.0<αi_(W)<20.0  (1)n₁₁≧1.9  (I-2)0.1<(n ₁₁−1)·(n ₁₂−1)·d·f _(W)/(r ₁₂ ·r ₂₁)<0.3  (5) (wherein,3.2<f_(T)/f_(W) and ω_(W)>35) where, αi_(W) is an incident angle of aprincipal ray to an image sensor at a maximum image height at awide-angle limit (defined as positive when the principal ray is incidenton a light acceptance surface of the image sensor in a state ofdeparting from the optical axis), n₁₁ is a refractive index of the firstlens element to the d-line, n₁₂ is a refractive index of the second lenselement to the d-line, r₁₂ is a radius of curvature of the image sidesurface of the first lens element, r₂₁ is a radius of curvature of theobject side surface of the second lens element, d is an optical axialdistance between the image side surface of the first lens element andthe object side surface of the second lens element, ω_(W) is a half viewangle (°) at a wide-angle limit, f_(T) is a focal length of the entiresystem at a telephoto limit, and f_(W) is a focal length of the entiresystem at a wide-angle limit.
 2. The zoom lens system as claimed inclaim 1, satisfying the following condition (I-3):0.8<(n ₁₁−1)²<1.5  (I-3) (wherein, 3.2<f_(T)/f_(W) and ω_(W)>35) where,n₁₁ is a refractive index of the first lens element to the d-line, ω_(W)is a half view angle (°) at a wide-angle limit, f_(T) is a focal lengthof the entire system at a telephoto limit, and f_(W) is a focal lengthof the entire system at a wide-angle limit.
 3. The zoom lens system asclaimed in claim 1, satisfying the following condition (I-4):0.75<(n ₁₁−1)·f _(W) /r ₁₂<1.2  (I-4) (wherein, 3.2<f_(T)/f_(W) andω_(W)>35) where, r₁₂ is a radius of curvature of the image side surfaceof the first lens element, n₁₁ is a refractive index of the first lenselement to the d-line, ω_(W) is a half view angle (°) at a wide-anglelimit, f_(T) is a focal length of the entire system at a telephotolimit, and f_(W) is a focal length of the entire system at a wide-anglelimit.
 4. The zoom lens system as claimed in claim 1, satisfying thefollowing condition (6):0.0001<(n ₁₁−1)·(n ₁₂−1)·d ² ·f _(W)/(r ₁₂ ·r ₂₁ ·f _(t))<0.04  (6)(wherein, 3.2<f_(T)/f_(W) and ω_(W)>35) where, n₁₁ is a refractive indexof the first lens element to the d-line, n₁₂ is a refractive index ofthe second lens element to the d-line, r₁₂ is a radius of curvature ofthe image side surface of the first lens element, r₂₁ is a radius ofcurvature of the object side surface of the second lens element, d is anoptical axial distance between the image side surface of the first lenselement and the object side surface of the second lens element, ω_(W) isa half view angle (°) at a wide-angle limit, f_(T) is a focal length ofthe entire system at a telephoto limit, and f_(W) is a focal length ofthe entire system at a wide-angle limit.
 5. The zoom lens system asclaimed in claim 1, satisfying the following condition (9):2.4<|f _(G1) |/f _(W)<4.0  (9) (wherein, 3.2<f_(T)/f_(W) and ω_(W)>35)where, f_(G1) is a composite focal length of the first lens unit, ω_(W)is a half view angle (°) at a wide-angle limit, f_(T) is a focal lengthof the entire system at a telephoto limit, and f_(W) is a focal lengthof the entire system at a wide-angle limit.
 6. The zoom lens system asclaimed in claim 1, satisfying the following condition (10):1.85<f _(G2) /f _(W)<3.0  (10) (wherein, 3.2<f_(T)/f_(W) and ω_(W)>35)where, f_(G2) is a composite focal length of the second lens unit, ω_(W)is a half view angle (°) at a wide-angle limit, f_(T) is a focal lengthof the entire system at a telephoto limit, and f_(W) is a focal lengthof the entire system at a wide-angle limit.
 7. The zoom lens system asclaimed in claim 1, satisfying the following condition (11):2.5<f _(G3) /f _(W)<6.0  (11) (wherein, 3.2<f_(T)/f_(W) and ω_(W)>35)where, f_(G3) is a composite focal length of the third lens unit, ω_(W)is a half view angle (°) at a wide-angle limit, f_(T) is a focal lengthof the entire system at a telephoto limit, and f_(W) is a focal lengthof the entire system at a wide-angle limit.
 8. The zoom lens system asclaimed in claim 1, satisfying the following condition (12):1.0<|f _(L1) |/f _(W)<2.5  (12) (wherein, 3.2<f_(T)/f_(W) and ω_(W)>35)where, f_(L1) is a focal length of the first lens element, ω_(W) is ahalf view angle (°) at a wide-angle limit, f_(T) is a focal length ofthe entire system at a telephoto limit, and f_(W) is a focal length ofthe entire system at a wide-angle limit.
 9. The zoom lens system asclaimed in claim 1, satisfying the following condition (13):2.0<f _(L2) /f _(W)<5.0  (13) (wherein, 3.2<f_(T)/f_(W) and ω_(W)>35)where, f_(L2) is a focal length of the second lens element, ω_(W) is ahalf view angle (°) at a wide-angle limit, f_(T) is a focal length ofthe entire system at a telephoto limit, and f_(W) is a focal length ofthe entire system at a wide-angle limit.
 10. The zoom lens system asclaimed in claim 1, satisfying the following condition (14):0.4<|f _(L1) |/|f _(G1)|<0.8  (14) (wherein, 3.2<f_(T)/f_(W) andω_(W)>35) where, f_(L1) is a focal length of the first lens element,f_(G1) is a composite focal length of the first lens unit, ω_(W) is ahalf view angle (°) at a wide-angle limit, f_(T) is a focal length ofthe entire system at a telephoto limit, and f_(W) is a focal length ofthe entire system at a wide-angle limit.
 11. The zoom lens system asclaimed in claim 1, satisfying the following condition (15):0.85<f _(L2) /|f _(G1)|<2.0  (15) (wherein, 3.2<f_(T)/f_(W) andω_(W)>35) where, f_(L2) is a focal length of the second lens element,f_(G1) is a composite focal length of the first lens unit, ω_(W) is ahalf view angle (°) at a wide-angle limit, f_(T) is a focal length ofthe entire system at a telephoto limit, and f_(W) is a focal length ofthe entire system at a wide-angle limit.
 12. The zoom lens system asclaimed in claim 1, satisfying the following condition (16):1.9<f _(L2) /|f _(L1)|<3.0  (16) (wherein, 3.2<f_(T)/f_(W) and ω_(W)>35)where, f_(L1) is a focal length of the first lens element, f_(L2) is afocal length of the second lens element, ω_(W) is a half view angle (°)at a wide-angle limit, f_(T) is a focal length of the entire system at atelephoto limit, and f_(W) is a focal length of the entire system at awide-angle limit.
 13. The zoom lens system as claimed in claim 1,wherein the second lens unit moves in a direction perpendicular to theoptical axis.
 14. An imaging device capable of outputting an opticalimage of an object as an electric image signal, comprising: a zoom lenssystem that forms the optical image of the object; and an image sensorthat converts the optical image formed by the zoom lens system into theelectric image signal, wherein in the zoom lens system, the system, inorder from the object side to the image side, comprises a first lensunit having negative optical power, a second lens unit having positiveoptical power and a third lens unit having positive optical power,wherein the first lens unit, in order from the object side to the imageside, consists of a first lens element that has a concave surface atleast on the image side and that has negative optical power and a secondlens element that has a convex surface at least on the object side andthat has positive optical power, the second lens unit, in order from theobject side to the image side, comprises a third lens element being onesingle lens element, a cemented lens element fabricated by cementing afourth lens element and a fifth lens element having optical power ofmutually different signs, and a sixth lens element being one single lenselement, in zooming from a wide-angle limit to a telephoto limit, all ofthe first lens unit, the second lens unit and the third lens unit movealong an optical axis, and the following conditions (1), (I-2) and (5)are satisfied:5.0<αi_(W)<20.0  (1)n₁₁≧1.9  (I-2)0.1<(n ₁₁−1)·(n ₁₂−1)·d·f _(W)/(r ₁₂ ·r ₂₁)<0.3  (5) (wherein,3.2<f_(T)/f_(W) and ω_(W)>35) where, αi_(W) is an incident angle of aprincipal ray to an image sensor at a maximum image height at awide-angle limit (defined as positive when the principal ray is incidenton a light acceptance surface of the image sensor in a state ofdeparting from the optical axis), n₁₁ is a refractive index of the firstlens element to the d-line, n₁₂ is a refractive index of the second lenselement to the d-line, r₁₂ is a radius of curvature of the image sidesurface of the first lens element, r₂₁ is a radius of curvature of theobject side surface of the second lens element, d is an optical axialdistance between the image side surface of the first lens element andthe object side surface of the second lens element, ω_(W) is a half viewangle (°) at a wide-angle limit, f_(T) is a focal length of the entiresystem at a telephoto limit, and f_(W) is a focal length of the entiresystem at a wide-angle limit.
 15. A camera for converting an opticalimage of an object into an electric image signal and then performing atleast one of displaying and storing of the converted image signal,comprising an imaging device having a zoom lens system that forms theoptical image of the object and an image sensor that converts theoptical image formed by the zoom lens system into the electric imagesignal, wherein in the zoom lens system, the system, in order from theobject side to the image side, comprises a first lens unit havingnegative optical power, a second lens unit having positive optical powerand a third lens unit having positive optical power, wherein the firstlens unit, in order from the object side to the image side, consists ofa first lens element that has a concave surface at least on the imageside and that has negative optical power and a second lens element thathas a convex surface at least on the object side and that has positiveoptical power, the second lens unit, in order from the object side tothe image side, comprises a third lens element being one single lenselement, a cemented lens element fabricated by cementing a fourth lenselement and a fifth lens element having optical power of mutuallydifferent signs, and a sixth lens element being one single lens element,in zooming from a wide-angle limit to a telephoto limit, all of thefirst lens unit, the second lens unit and the third lens unit move alongan optical axis, and the following conditions (1), (I-2) and (5) aresatisfied:5.0<αi_(W)<20.0  (1)n₁₁≧1.9  (I-2)0.1<(n ₁₁−1)·(n ₁₂−1)·d·f _(W)/(r ₁₂ ·r ₂₁)<0.3  (5) (wherein,3.2<f_(T)/f_(W) and ω_(W)>35) where, αi_(W) is an incident angle of aprincipal ray to an image sensor at a maximum image height at awide-angle limit (defined as positive when the principal ray is incidenton a light acceptance surface of the image sensor in a state ofdeparting from the optical axis), n₁₁ is a refractive index of the firstlens element to the d-line, n₁₂ is a refractive index of the second lenselement to the d-line, r₁₂ is a radius of curvature of the image sidesurface of the first lens element, r₂₁ is a radius of curvature of theobject side surface of the second lens element, d is an optical axialdistance between the image side surface of the first lens element andthe object side surface of the second lens element, ω_(W) is a half viewangle (°) at a wide-angle limit, f_(T) is a focal length of the entiresystem at a telephoto limit, and f_(W) is a focal length of the entiresystem at a wide-angle limit.
 16. A zoom lens system, in order from theobject side to the image side, comprising a first lens unit havingnegative optical power, a second lens unit having positive optical powerand a third lens unit having positive optical power, wherein the firstlens unit, in order from the object side to the image side, consists ofa first lens element that has a concave surface at least on the imageside and that has negative optical power and a second lens element thathas a convex surface at least on the object side and that has positiveoptical power, the second lens unit, in order from the object side tothe image side, comprises a third lens element being one single lenselement, a cemented lens element fabricated by cementing a fourth lenselement and a fifth lens element having optical power of mutuallydifferent signs, and a sixth lens element being one single lens element,in zooming from a wide-angle limit to a telephoto limit, all of thefirst lens unit, the second lens unit and the third lens unit move alongan optical axis, and the following conditions (1), (II-2) and (5) aresatisfied:5.0<αi_(W)<20.0  (1)(n ₁₁−1)·(n ₁₂−1)≧0.84  (II-2)0.1<(n ₁₁−1)·(n ₁₂−1)·d·f _(W)/(r ₁₂ ·r ₂₁)<0.3  (5) (wherein,3.2<f_(T)/f_(W) and ω_(W)>35) where, αi_(W) is an incident angle of aprincipal ray to an image sensor at a maximum image height at awide-angle limit (defined as positive when the principal ray is incidenton a light acceptance surface of the image sensor in a state ofdeparting from the optical axis), n₁₁ is a refractive index of the firstlens element to the d-line, n₁₂ is a refractive index of the second lenselement to the d-line, r₁₂ is a radius of curvature of the image sidesurface of the first lens element, r₂₁ is a radius of curvature of theobject side surface of the second lens element, d is an optical axialdistance between the image side surface of the first lens element andthe object side surface of the second lens element, ω_(W) is a half viewangle (°) at a wide-angle limit, f_(T) is a focal length of the entiresystem at a telephoto limit, and f_(W) is a focal length of the entiresystem at a wide-angle limit.
 17. The zoom lens system as claimed inclaim 16, satisfying the following condition (6):0.0001<(n ₁₁−1)·(n ₁₂−1)·d ² ·f _(W)/(r ₁₂ ·r ₂₁ ·f _(t))<0.04  (6)(wherein, 3.2<f_(T)/f_(W) and ω_(W)>35) where, n₁₁ is a refractive indexof the first lens element to the d-line, n₁₂ is a refractive index ofthe second lens element to the d-line, r₁₂ is a radius of curvature ofthe image side surface of the first lens element, r₂₁ is a radius ofcurvature of the object side surface of the second lens element, d is anoptical axial distance between the image side surface of the first lenselement and the object side surface of the second lens element, ω_(W) isa half view angle (°) at a wide-angle limit, f_(T) is a focal length ofthe entire system at a telephoto limit, and f_(W) is a focal length ofthe entire system at a wide-angle limit.
 18. The zoom lens system asclaimed in claim 16, satisfying the following condition (9):2.4<|f _(G1) |/f _(W)<4.0  (9) (wherein, 3.2<f_(T)/f_(W) and ω_(W)>35)where, f_(G1) is a composite focal length of the first lens unit, ω_(W)is a half view angle (°) at a wide-angle limit, f_(T) is a focal lengthof the entire system at a telephoto limit, and f_(W) is a focal lengthof the entire system at a wide-angle limit.
 19. The zoom lens system asclaimed in claim 16, satisfying the following condition (10):1.85<f _(G2) /f _(W)<3.0  (10) (wherein, 3.2<f_(T)/f_(W) and ω_(W)>35)where, f_(G2) is a composite focal length of the second lens unit, ω_(W)is a half view angle (°) at a wide-angle limit, f_(T) is a focal lengthof the entire system at a telephoto limit, and f_(W) is a focal lengthof the entire system at a wide-angle limit.
 20. The zoom lens system asclaimed in claim 16, satisfying the following condition (11):2.5<f _(G3) /f _(W)<6.0  (11) (wherein, 3.2<f_(T)/f_(W) and ω_(W)>35)where, f_(G3) is a composite focal length of the third lens unit, ω_(W)is a half view angle (°) at a wide-angle limit, f_(T) is a focal lengthof the entire system at a telephoto limit, and f_(W) is a focal lengthof the entire system at a wide-angle limit.
 21. The zoom lens system asclaimed in claim 16, satisfying the following condition (12):1.0<|f _(L1) |/f _(W)<2.5  (12) (wherein, 3.2<f_(T)/f_(W) and ω_(W)>35)where, f_(L1) is a focal length of the first lens element, ω_(W) is ahalf view angle (°) at a wide-angle limit, f_(T) is a focal length ofthe entire system at a telephoto limit, and f_(W) is a focal length ofthe entire system at a wide-angle limit.
 22. The zoom lens system asclaimed in claim 16, satisfying the following condition (13):2.0<f _(L2) /f _(W)<5.0  (13) (wherein, 3.2<f_(T)/f_(W) and ω_(W)>35)where, f_(L2) is a focal length of the second lens element, ω_(W) is ahalf view angle (°) at a wide-angle limit, f_(T) is a focal length ofthe entire system at a telephoto limit, and f_(W) is a focal length ofthe entire system at a wide-angle limit.
 23. The zoom lens system asclaimed in claim 16, satisfying the following condition (14):0.4<|f _(L1) |/|f _(G1)|<0.8  (14) (wherein, 3.2<f_(T)/f_(W) andω_(W)>35) where, f_(L1) is a focal length of the first lens element,f_(G1) is a composite focal length of the first lens unit, ω_(W) is ahalf view angle (°) at a wide-angle limit, f_(T) is a focal length ofthe entire system at a telephoto limit, and f_(W) is a focal length ofthe entire system at a wide-angle limit.
 24. The zoom lens system asclaimed in claim 16, satisfying the following condition (15):0.85<f _(L2) /|f _(G1)|<2.0  (15) (wherein, 3.2<f_(T)/f_(W) andω_(W)>35) where, f_(L2) is a focal length of the second lens element,f_(G1) is a composite focal length of the first lens unit, ω_(W) is ahalf view angle (°) at a wide-angle limit, f_(T) is a focal length ofthe entire system at a telephoto limit, and f_(W) is a focal length ofthe entire system at a wide-angle limit.
 25. The zoom lens system asclaimed in claim 16, satisfying the following condition (16):1.9<f _(L2) /|f _(L1)|<3.0  (16) (wherein, 3.2<f_(T)/f_(W) and ω_(W)>35)where, f_(L1) is a focal length of the first lens element, f_(L2) is afocal length of the second lens element, ω_(W) is a half view angle (°)at a wide-angle limit, f_(T) is a focal length of the entire system at atelephoto limit, and f_(W) is a focal length of the entire system at awide-angle limit.
 26. The zoom lens system as claimed in claim 16,wherein the second lens unit moves in a direction perpendicular to theoptical axis.
 27. An imaging device capable of outputting an opticalimage of an object as an electric image signal, comprising: a zoom lenssystem that forms the optical image of the object; and an image sensorthat converts the optical image formed by the zoom lens system into theelectric image signal, wherein in the zoom lens system, the system, inorder from the object side to the image side, comprises a first lensunit having negative optical power, a second lens unit having positiveoptical power and a third lens unit having positive optical power,wherein the first lens unit, in order from the object side to the imageside, consists of a first lens element that has a concave surface atleast on the image side and that has negative optical power and a secondlens element that has a convex surface at least on the object side andthat has positive optical power, the second lens unit, in order from theobject side to the image side, comprises a third lens element being onesingle lens element, a cemented lens element fabricated by cementing afourth lens element and a fifth lens element having optical power ofmutually different signs, and a sixth lens element being one single lenselement, in zooming from a wide-angle limit to a telephoto limit, all ofthe first lens unit, the second lens unit and the third lens unit movealong an optical axis, and the following conditions (1), (II-2) and (5)are satisfied:5.0<αi_(W)<20.0  (1)(n ₁₁−1)·(n ₁₂−1)≧0.84  (II-2)0.1<(n ₁₁−1)·(n ₁₂−1)·d·f _(W)/(r ₁₂ ·r ₂₁)<0.3  (5) (wherein,3.2<f_(T)/f_(W) and ω_(W)>35) where, αi_(W) is an incident angle of aprincipal ray to an image sensor at a maximum image height at awide-angle limit (defined as positive when the principal ray is incidenton a light acceptance surface of the image sensor in a state ofdeparting from the optical axis), n₁₁ is a refractive index of the firstlens element to the d-line, n₁₂ is a refractive index of the second lenselement to the d-line, r₁₂ is a radius of curvature of the image sidesurface of the first lens element, r₂₁ is a radius of curvature of theobject side surface of the second lens element, d is an optical axialdistance between the image side surface of the first lens element andthe object side surface of the second lens element, ω_(W) is a half viewangle (°) at a wide-angle limit, f_(T) is a focal length of the entiresystem at a telephoto limit, and f_(W) is a focal length of the entiresystem at a wide-angle limit.
 28. A camera for converting an opticalimage of an object into an electric image signal and then performing atleast one of displaying and storing of the converted image signal,comprising an imaging device having a zoom lens system that forms theoptical image of the object and an image sensor that converts theoptical image formed by the zoom lens system into the electric imagesignal, wherein in the zoom lens system, the system, in order from theobject side to the image side, comprises a first lens unit havingnegative optical power, a second lens unit having positive optical powerand a third lens unit having positive optical power, wherein the firstlens unit, in order from the object side to the image side, consists ofa first lens element that has a concave surface at least on the imageside and that has negative optical power and a second lens element thathas a convex surface at least on the object side and that has positiveoptical power, the second lens unit, in order from the object side tothe image side, comprises a third lens element being one single lenselement, a cemented lens element fabricated by cementing a fourth lenselement and a fifth lens element having optical power of mutuallydifferent signs, and a sixth lens element being one single lens element,in zooming from a wide-angle limit to a telephoto limit, all of thefirst lens unit, the second lens unit and the third lens unit move alongan optical axis, and the following conditions (1), (II-2) and (5) aresatisfied:5.0<αi_(W)<20.0  (1)(n ₁₁−1)·(n ₁₂−1)≧0.84  (II-2)0.1<(n ₁₁−1)·(n ₁₂−1)·d·f _(W)/(r ₁₂ ·r ₂₁)<0.3  (5) (wherein,3.2<f_(T)/f_(W) and ω_(W)>35) where, αi_(W) is an incident angle of aprincipal ray to an image sensor at a maximum image height at awide-angle limit (defined as positive when the principal ray is incidenton a light acceptance surface of the image sensor in a state ofdeparting from the optical axis), n₁₁ is a refractive index of the firstlens element to the d-line, n₁₂ is a refractive index of the second lenselement to the d-line, r₁₂ is a radius of curvature of the image sidesurface of the first lens element, r₂₁ is a radius of curvature of theobject side surface of the second lens element, d is an optical axialdistance between the image side surface of the first lens element andthe object side surface of the second lens element, ω_(W) is a half viewangle (°) at a wide-angle limit, f_(T) is a focal length of the entiresystem at a telephoto limit, and f_(W) is a focal length of the entiresystem at a wide-angle limit.
 29. A zoom lens system, in order from theobject side to the image side, comprising a first lens unit havingnegative optical power, a second lens unit having positive optical powerand a third lens unit having positive optical power, wherein the firstlens unit, in order from the object side to the image side, consists ofa first lens element that has a concave surface at least on the imageside and that has negative optical power and a second lens element thathas a convex surface at least on the object side and that has positiveoptical power, the second lens unit, in order from the object side tothe image side, comprises a third lens element being one single lenselement, a cemented lens element fabricated by cementing a fourth lenselement and a fifth lens element having optical power of mutuallydifferent signs, and a sixth lens element being one single lens element,in zooming from a wide-angle limit to a telephoto limit, all of thefirst lens unit, the second lens unit and the third lens unit move alongan optical axis, and the following conditions (1), (III-2) and (5) aresatisfied:5.0<αi_(W)<20.0  (1)n₁₂≧2.1  (III-2)0.1<(n ₁₁−1)·(n ₁₂−1)·d·f _(W)/(r ₁₂ ·r ₂₁)<0.3  (5) (wherein,3.2<f_(T)/f_(W) and ω_(W)>35) where, αi_(W) is an incident angle of aprincipal ray to an image sensor at a maximum image height at awide-angle limit (defined as positive when the principal ray is incidenton a light acceptance surface of the image sensor in a state ofdeparting from the optical axis), n₁₁ is a refractive index of the firstlens element to the d-line, n₁₂ is a refractive index of the second lenselement to the d-line, r₁₂ is a radius of curvature of the image sidesurface of the first lens element, r₂₁ is a radius of curvature of theobject side surface of the second lens element, d is an optical axialdistance between the image side surface of the first lens element andthe object side surface of the second lens element, ω_(W) is a half viewangle (°) at a wide-angle limit, f_(T) is a focal length of the entiresystem at a telephoto limit, and f_(W) is a focal length of the entiresystem at a wide-angle limit.
 30. The zoom lens system as claimed inclaim 29, satisfying the following condition (III-3):0.8<(n ₁₂−1)²<1.5  (III-3) (wherein, 3.2<f_(T)/f_(W) and ω_(W)>35)where, n₁₂ is a refractive index of the second lens element to thed-line, ω_(W) is a half view angle (°) at a wide-angle limit, f_(T) is afocal length of the entire system at a telephoto limit, and f_(W) is afocal length of the entire system at a wide-angle limit.
 31. The zoomlens system as claimed in claim 29, satisfying the following condition(III-4):0.4<(n ₁₂−1)·f _(W) /r ₂₁<0.7  (III-4) (wherein, 3.2<f_(T)/f_(W) andω_(W)>35) where, r₂₁ is a radius of curvature of the object side surfaceof the second lens element, n₁₂ is a refractive index of the second lenselement to the d-line, ω_(W) is a half view angle (°) at a wide-anglelimit, f_(T) is a focal length of the entire system at a telephotolimit, and f_(W) is a focal length of the entire system at a wide-anglelimit.
 32. The zoom lens system as claimed in claim 29, satisfying thefollowing condition (6):0.0001<(n ₁₁−1)·(n ₁₂−1)·d ² f _(W)/(r ₁₂ ·r ₂₁ ·f _(t))<0.04  (6)(wherein, 3.2<f_(T)/f_(W) and ω_(W)>35) where, n₁₁ is a refractive indexof the first lens element to the d-line, n₁₂ is a refractive index ofthe second lens element to the d-line, r₁₂ is a radius of curvature ofthe image side surface of the first lens element, r₂₁ is a radius ofcurvature of the object side surface of the second lens element, d is anoptical axial distance between the image side surface of the first lenselement and the object side surface of the second lens element, ω_(W) isa half view angle (°) at a wide-angle limit, f_(T) is a focal length ofthe entire system at a telephoto limit, and f_(W) is a focal length ofthe entire system at a wide-angle limit.
 33. The zoom lens system asclaimed in claim 29, satisfying the following condition (9):2.4<|f _(G1) |/f _(W)<4.0  (9) (wherein, 3.2<f_(T)/f_(W) and ω_(W)>35)where, f_(G1) is a composite focal length of the first lens unit, ω_(W)is a half view angle (°) at a wide-angle limit, f_(T) is a focal lengthof the entire system at a telephoto limit, and f_(W) is a focal lengthof the entire system at a wide-angle limit.
 34. The zoom lens system asclaimed in claim 29, satisfying the following condition (10):1.85<f _(G2) /f _(W)<3.0  (10) (wherein, 3.2<f_(T)/f_(W) and ω_(W)>35)where, f_(G2) is a composite focal length of the second lens unit, ω_(W)is a half view angle (°) at a wide-angle limit, f_(T) is a focal lengthof the entire system at a telephoto limit, and f_(W) is a focal lengthof the entire system at a wide-angle limit.
 35. The zoom lens system asclaimed in claim 29, satisfying the following condition (11):2.5<f _(G3) /f _(W)<6.0  (11) (wherein, 3.2<f_(T)/f_(W) and ω_(W)>35)where, f_(G3) is a composite focal length of the third lens unit, ω_(W)is a half view angle (°) at a wide-angle limit, f_(T) is a focal lengthof the entire system at a telephoto limit, and f_(W) is a focal lengthof the entire system at a wide-angle limit.
 36. The zoom lens system asclaimed in claim 29, satisfying the following condition (12):1.0<|f _(L1) |/f _(W)<2.5  (12) (wherein, 3.2<f_(T)/f_(W) and ω_(W)>35)where, f_(L1) is a focal length of the first lens element, ω_(W) is ahalf view angle (°) at a wide-angle limit, f_(T) is a focal length ofthe entire system at a telephoto limit, and f_(W) is a focal length ofthe entire system at a wide-angle limit.
 37. The zoom lens system asclaimed in claim 29, satisfying the following condition (13):2.0<f _(L2) /f _(W)<5.0  (13) (wherein, 3.2<f_(T)/f_(W) and ω_(W)>35)where, f_(L2) is a focal length of the second lens element, ω_(W) is ahalf view angle (°) at a wide-angle limit, f_(T) is a focal length ofthe entire system at a telephoto limit, and f_(W) is a focal length ofthe entire system at a wide-angle limit.
 38. The zoom lens system asclaimed in claim 29, satisfying the following condition (14):0.4<|f _(L1) |/|f _(G1)|<0.8  (14) (wherein, 3.2<f_(T)/f_(W) andω_(W)>35) where, f_(L1) is a focal length of the first lens element,f_(G1) is a composite focal length of the first lens unit, ω_(W) is ahalf view angle (°) at a wide-angle limit, f_(T) is a focal length ofthe entire system at a telephoto limit, and f_(W) is a focal length ofthe entire system at a wide-angle limit.
 39. The zoom lens system asclaimed in claim 29, satisfying the following condition (15):0.85<f _(L2) /|f _(G1)|<2.0  (15) (wherein, 3.2<f_(T)/f_(W) andω_(W)>35) where, f_(L2) is a focal length of the second lens element,f_(G1) is a composite focal length of the first lens unit, ω_(W) is ahalf view angle (°) at a wide-angle limit, f_(T) is a focal length ofthe entire system at a telephoto limit, and f_(W) is a focal length ofthe entire system at a wide-angle limit.
 40. The zoom lens system asclaimed in claim 29, satisfying the following condition (16):1.9<f _(L2) /|f _(L1)|<3.0  (16) (wherein, 3.2<f_(T)/f_(W) and ω_(W)>35)where, f_(L1) is a focal length of the first lens element, f_(L2) is afocal length of the second lens element, ω_(W) is a half view angle (°)at a wide-angle limit, f_(T) is a focal length of the entire system at atelephoto limit, and f_(W) is a focal length of the entire system at awide-angle limit.
 41. The zoom lens system as claimed in claim 29,wherein the second lens unit moves in a direction perpendicular to theoptical axis.
 42. An imaging device capable of outputting an opticalimage of an object as an electric image signal, comprising: a zoom lenssystem that forms the optical image of the object; and an image sensorthat converts the optical image formed by the zoom lens system into theelectric image signal, wherein in the zoom lens system, the system, inorder from the object side to the image side, comprises a first lensunit having negative optical power, a second lens unit having positiveoptical power and a third lens unit having positive optical power,wherein the first lens unit, in order from the object side to the imageside, consists of a first lens element that has a concave surface atleast on the image side and that has negative optical power and a secondlens element that has a convex surface at least on the object side andthat has positive optical power, the second lens unit, in order from theobject side to the image side, comprises a third lens element being onesingle lens element, a cemented lens element fabricated by cementing afourth lens element and a fifth lens element having optical power ofmutually different signs, and a sixth lens element being one single lenselement, in zooming from a wide-angle limit to a telephoto limit, all ofthe first lens unit, the second lens unit and the third lens unit movealong an optical axis, and the following conditions (1), (III-2) and (5)are satisfied:5.0<αi_(W)<20.0  (1)n₁₂≧2.1  (III-2)0.1<(n ₁₁−1)·(n ₁₂−1)·d·f _(W)/(r ₁₂ ·r ₂₁)<0.3  (5) (wherein,3.2<f_(T)/f_(W) and ω_(W)>35) where, αi_(W) is an incident angle of aprincipal ray to an image sensor at a maximum image height at awide-angle limit (defined as positive when the principal ray is incidenton a light acceptance surface of the image sensor in a state ofdeparting from the optical axis), n₁₁ is a refractive index of the firstlens element to the d-line, n₁₂ is a refractive index of the second lenselement to the d-line, r₁₂ is a radius of curvature of the image sidesurface of the first lens element, r₂₁ is a radius of curvature of theobject side surface of the second lens element, d is an optical axialdistance between the image side surface of the first lens element andthe object side surface of the second lens element, ω_(W) is a half viewangle (°) at a wide-angle limit, f_(T) is a focal length of the entiresystem at a telephoto limit, and f_(W) is a focal length of the entiresystem at a wide-angle limit.
 43. A camera for converting an opticalimage of an object into an electric image signal and then performing atleast one of displaying and storing of the converted image signal,comprising an imaging device having a zoom lens system that forms theoptical image of the object and an image sensor that converts theoptical image formed by the zoom lens system into the electric imagesignal, wherein in the zoom lens system, the system, in order from theobject side to the image side, comprises a first lens unit havingnegative optical power, a second lens unit having positive optical powerand a third lens unit having positive optical power, wherein the firstlens unit, in order from the object side to the image side, consists ofa first lens element that has a concave surface at least on the imageside and that has negative optical power and a second lens element thathas a convex surface at least on the object side and that has positiveoptical power, the second lens unit, in order from the object side tothe image side, comprises a third lens element being one single lenselement, a cemented lens element fabricated by cementing a fourth lenselement and a fifth lens element having optical power of mutuallydifferent signs, and a sixth lens element being one single lens element,in zooming from a wide-angle limit to a telephoto limit, all of thefirst lens unit, the second lens unit and the third lens unit move alongan optical axis, and the following conditions (1), (III-2) and (5) aresatisfied:5.0<αi_(W)<20.0  (1)n₁₂≧2.1  (III-2)0.1<(n ₁₁−1)·(n ₁₂−1)·d·f _(W)/(r ₁₂ ·r ₂₁)<0.3  (5) (wherein,3.2<f_(T)/f_(W) and ω_(W)>35) where, αi_(W) is an incident angle of aprincipal ray to an image sensor at a maximum image height at awide-angle limit (defined as positive when the principal ray is incidenton a light acceptance surface of the image sensor in a state ofdeparting from the optical axis), n₁₁ is a refractive index of the firstlens element to the d-line, n₁₂ is a refractive index of the second lenselement to the d-line, r₁₂ is a radius of curvature of the image sidesurface of the first lens element, r₂₁ is a radius of curvature of theobject side surface of the second lens element, d is an optical axialdistance between the image side surface of the first lens element andthe object side surface of the second lens element, ω_(W) is a half viewangle (°) at a wide-angle limit, f_(T) is a focal length of the entiresystem at a telephoto limit, and f_(W) is a focal length of the entiresystem at a wide-angle limit.